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/^ iZuZd^. M*<>«'«»'^ 




The Gray Squirrel. 

(Courtesy of F. H. Tucker, Boston.) 



Zoology 



A 



A Textbook for College and 
U?tiverstty Students 



By 

F. E. CHIDESTER, A.M., Ph.D. 

Professor of Zoology, West Virginia University 




NEW YORK 

D. VAN NOSTRAND COMPANY, Inc. 
250 Fourth Avenue 

1932 



'^3 



Copyright, ig32, 

by 

D. Fan Nostra?!^ Compa?iy, Inc. 



All Rights Reserved. 

This book or any parts thereof may not 
be reproduced in any form without 
written permission from the publishers. 



PRINTED IN U. S. A. 



LANCASTER PRESS, INC. 
LANCASTER, PA. 



To the Student who uses this TexthooX: 

This textbook represents many years of 
learning and experience on the part of the 
author. It does not treat of an ephemeral 
subject, but one which, since you are study- 
ing it in college, you must feel will have a 
use to you in your future life. 

Unquestionably you will many times in 
later life wish to refer to specific details 
and facts about the subject which this book 
covers and which you may forget. How 
better could you find this information than 
in the textbook which you have studied from 
cover to cover? 

Retain it for your reference library. You 
will use it many times in the future. 

The Puhlishers. 



Dedicated to 
DR. AND MRS. C. W. CHIDESTER 

A RARE COMBINATION IN 

MEDICAL PRACTICE AND A CONSTANT SOURCE OF 

STIMULATION TO SCIENTIFIC EFFORT 



PREFACE 

This text was written as a general survey of modern zoology for 
use by college students and to serve as a reference book for biologists. 
In the author's attempt to include in the introductory course not 
only the basic principles so obviously essential to a general culture 
course in animal biology, but also to satisfy the needs of students 
entering medicine and agriculture, he has found it desirable to em- 
phasize physiology, ecology and applied zoology. Many of the 
most interesting portions of this text have been introduced as a 
result of inquiries by keen students. 

After using much of the subject matter as a mimeographed text, 
the author prepared the manuscript in its final form, and during 
three summers has availed himself of the aid of many specialists 
at the Marine Biological Laboratory, Woods Hole, Mass. Through 
the interest of various authorities who gave advance information 
about their work, certain chapters include material prior to the 
actual publication of the research discussed. 

Some of the most important features of the book are the logical 
arrangement of facts about the animals within a group, a statement 
of the chief characteristics at the beginning of the discussion, and a 
summary on the economic importance at the end of each section. 
The newer physiology has been introduced and a bibliography 
checked by experts in each field is given at the end of each chapter. 
Sources readily available have been selected and resumes chosen 
instead of the pioneer researches. Extensive discussions of Embry- 
ology and Animal Behavior have been found undesirable since such 
studies cannot be comprehensively treated in an introductory course 
without excluding other fundamental subjects. 

The writer takes pleasure in thanking the following colleagues 
at West Virginia University: Dr. A. M. Reese, Dr. L. H. Taylor, 
Mr. A. G. Eaton, Dr. L. H. Peairs, Dr. A. J. Dadisman, Mr. Chan- 
dler Brooks, Dr. J. A. Eiesland, Dr. P. D. Strausbaugh, Dr. A. J. 
Hare, Dr. F. B. Trotter and Dr. C. G. Brouzas. 

Certain chapters have, furthermore, received the benefit of criti- 
cism by the following specialists: Dr. G. N. Calkins and Dr. C. A. 
Kofoid, Protozoa; Dr. M. M. Metcalf, Evolution; Dr. C. E. Mc- 



vi PREFACE 

Clung and Dr. E. Carothers, Cytology; Dr. A. B. Dawson, Blood; 
Dr. A. C. Redfield, Respiratory Pigments; Dr. A. M. Lucas, Ciliary 
Action; Dr. Edwin Linton, Dr. C. A. Kofoid, and Dr. H. W. Stunk- 
ard, Platyhelminthes; Dr. Frank Smith and Dr. Earl Martin, 
Annelida; Dr. N. A. Cobb, Dr. M. C. Hall, Dr. C. A. Kofoid, 
Nematoda; Dr. R. S. Lynch, Dr. H. M. Miller and Dr. H. B. Smith, 
Trochelminthes; Dr. B. H. Grave and Dr. E. D. Crabb, Mollusca. 
Dr. C. M. Child, Dr. Austin Clark and Dr. William Patten have 
kindly furnished concise summaries of their important theories. 

With the aid of their staffs the following Librarians, Mr. George 
Osborn, Rutgers University, Dr. L. D. Arnett, West Virginia 
University, and Mrs. T. H. Montgomery, Marine Biological Lab- 
oratory, have so contributed to the accuracy of the text by their 
tireless efforts in furnishing reprints, references and books that they 
deserve much of the credit for such corrections of errors made by 
senior scholars as the author may have been able to make. 

Dr. W. H. S. Demarest, Dr. F. B. Trotter, and Dr. J. R. Turner, 
the University Presidents under whom the writer enjoyed every 
opportunity for effective teaching that these able executives could 
possibly furnish, should be heartily thanked for their aid. 

The writer also wishes to acknowledge his indebtedness to: the 
late Dr. C. W. Hargitt, Dr. W. M. Smallwood, Dr. C. F. Hodge, Dr. 
A. M. Reese, Dr. F. R. Lillie, Dr. E. G. Conklin, Dr. C. B. Daven- 
port, Dr. T. J. Headlee, Dr. Gary Calkins and Dr. C. E. McClung. 
By their encouragement, these men have been largely responsible 
for the vigor and enthusiasm with which the writer has been able 
to study zoological problems and to teach his subject for more than 
twenty years. 

General criticism has been offered by Dr. J. A. Dawson, Dr. 
Mary MacDougall, Dr. W. C. Curtis, Dr D. H. Tennent, Dr. 
Charles Packard, Dr. R. A. Budington, Dr. W. L. DoUey, Dr. 
Oscar Richards, Dr. J. W. McGregor, Dr. J. W. Mavor, Dr. Leigh 
Hoadley, and many others. 

In the preparation of the glossary. Professor A. J. Hare of the 
West Virginia University has assumed the responsibility for the 
Greek and Latin derivations of the words used. 

The drawings were made by Mr. W. J. Moore, Mrs. Helena 
Lammers and Mr. Norris Jones. 

F. E. C. 

Woods Hole, Mass., 
November 1931 



CONTENTS 

Preface 
chapter page 

I — Introduction i 

The Function of Zoology — The Divisions of Zoology — Living Things 
Compared with Non-Living Matter — Protoplasm — Structure of the 
Cell — Structure of Protoplasm — Physiological Properties — Chemical 
Composition — Proteins — Carbohydrates — Fats — Water — Chemical 
Elements — Carbon — Hydrogen — Oxygen — Nitrogen — Sulphur — 
Mineral Salts, Enzymes, Hormones and Vitamins — Animal Relation- 
ships — Fitness to Survive — Plants and Animals — Table — Classification 
— Metazoa — Vertebrates — Phylum Chordata — Sub-phylum Vertebrata 
— Sub-phylum Adelochorda — Sub-phylum Urochorda — Invertebrates — 
Phylum Arthropoda — Phylum Mollusca — Phylum Molluscoidea — 
Phylum Trochelminthes — Phylum Annelida — Phylum Echinodermata 
— Phylum Nemathelminthes — Phylum Platyhelminthes — Phylum Coc- 
lenterata — Phylum Porifera — Phylum Protozoa. 

II — Protozoa 21 

Classification — Characteristics — Natural History — Class i. Sarcodina 
— Type of Group — Ameba proteus — Orders of Sarcodina — Parasitic 
Sarcodina — Class 2. Mastigophora (Flagellates) — Type of Group — 
Euglena — Economic Importance of Flagellates — Class 3. Infusoria 
(Ciliates) — Type of Group — Paramecium — Parasitic Ciliates — Class 4. 
Sporozoa — Type Plasmodium vivax,the Malarial Sporozoon — Orders of 
Sporozoa — General Considerations — External Anatomy and Internal 
Differentiation — Locomotion — Ingestion and Digestion — Respiration 
■ — Circulation — Excretion — Irritability — Reproduction and Regenera- 
tion — Sarcodina — Mastigophora (Flagellata) — Infusoria (Ciliata) — 
Sporozoa — Endomixis — Distribution — Economic Importance — Fossil 
Relatives and Relationship to Other Phyla — Metazoa. 

Ill — Porifera 47 

Classification — Characteristics — Distribution — Pigment in Sponges — 
Type of Group — Grantia — External Anatomy — Ingestion and Diges- 
tion—Circulation — Respiration — Excretion — Reproduction — Nervous 
System — Habits — Enemies — Associations — Economic Importance of 
the Porifera — Positive — Negative — Fossil Relatives — Ancestry and 
Relationship to Other Phyla. 

IV — Coelenterata 54 

Classification — Characteristics — Natural History — Class i. Hydrozoa 
— Hydra — Obelia — Alternation of Generations In the Hydrozoa — Si- 
phonophora — Class 2. Scyphozoa — Type of Group — Aurelia — Class 3. 
Actinozoa — Anemones and Corals — Class (or Phylum) Ctenophora — 

vii 



39371 



viii CONTENTS 

CHAPTER PAGE 

General Consideration of the Coelenterates — Distribution — Anatomy — 
Physiology — Habitat — Regeneration — Fossil Relatives — Ancestry and 
Relationship to Other Phyla — Economic Importance of Coelenterates. 

V — ^Platyhelminthes 71 

Classification — Characteristics — Natural History — Class i. Turbella- 
ria — Type of Group — Planaria — Class 2. Trematoda — Anatomy and 
Life History of the Liver Fluke — Trematode Parasites — Class 3. Ces- 
toda — Type of Group — Taenia solium — Cestode Parasites — General 
Consideration of the Platyhelminthes — Distribution — Anatomy and 
Physiology — Behavior — Regeneration — Fossil Relatives — Ancestry 
and Relationship to Other Phyla — Axial Gradient Theory of Child — 
Nemertinea, Possibly Allied to Platyhelminthes. 

VI — Nemathelminthes 87 

Classification — Characteristics — Natural History — Class Nematoda — 
Family i. Ascaridae — Tvpe of Group — Ascaris lumbricoides — Family 
2. Anguillidae — Life History of Caconema (Heterodera) radicicola — 
Family 3. Strongylidae — Life History of Necator americana — Family 
4. Trichotrachellidae— Family 5. Filarldae — Life History of Filaria 
bancrofti — Family 6. Trichinellidae — Life History of Trichinella 
spiralis — Uncertain Classes formerly placed under Nemathelminthes — 
Acanthocephala — Gordiaceae — Mermithidae — General Consideration 
of the Nemathelminthes — Distribution — Physiology — Fossil Relatives 
— Ancestry and Relationship to Other Phyla. 

VII— Annelida 100 

Classification — Characteristics — Natural History — Class i. Archi- 
Annelida — Polygordius — Class 2. Chaetopoda — Type of Group — 
Lumbricus terrestris — Conjugation in the Earthworm. Class 3. 
Hirudinea — Type of Group — Hirudo medicinalis — Adaptation of the 
Leech to its Mode of Life — General Consideration of the Annelida — 
Distribution and Habits— Parasites of the Annelida — Physiology, 
Anatomy, and Locomotion — Regeneration — Fossil Relatives — Ances- 
try and Relationship to Other Phyla — Economic Importance of An- 
nelida. 

VIII — Trochelminthes • . • • 121 

IX MOLLUSCOIDEA I 27 

Natural History— Class i. Brachiopoda— Class 2. Bryozoa (Polyzoa) 
— Class 3. Phoronidea. 

X ECHINODERMATA 1^9 

Classification — Characteristics — Natural History — Class i. Aste- 
roidea — Type of Group — Asterias — Artificial Parthenogenesis — Class 
2. Ophiuroidea — Class 3. Echinoidea — Class 4. Holothuroidea — 
General Considerations — Anatomy and Locomotion — Physiology — 
Behavior — Embryonic Development — Parental Care — Regeneration 



CONTENTS ix 

CHAPTER PAGE 

and Autotomy — Fossil Relatives — Ancestry and Relationship to Other 
Phyla — Economic Importance. 

XI— MoLLUscA 142 

Classification — Class i. Pelecypoda or Lamellibranchiata — Class 2. 
Amphineura — Class 3. Gastropoda — Class 4. Scaphopoda — Class 5. 
Cephalopoda — Characteristics — Natural History — Class i. Lamel- 
libranchiata — Types of Group — Clams and Mussels — Natural History 
of Lamellibranchiata — Class 2. Gastropoda — Natural History of Gas- 
tropoda — Class 3. Scaphopoda — Value of Dentalium — Class 4. Ceph- 
alopoda — Natural History — Pearls — Composition — Source and Value 
— Culture Pearls — Coated Glass Substitutes for Pearls — References — 
General Consideration of the Mollusca— Distribution— Physiology- 
Nervous System — Regeneration — Growth Studies of the iVIollusca — 
Embryology — Care of the Young — Fossil Relatives — Ancestry and 
Relationship to Other Phyla — Economic Importance of Mollusca — 
Positive — Negative. 

XII — Arthropoda '°3 

Classification— Characteristics— Natural History— Class i. Crustacea 
— Types— Crayfish and Lobster— Class 2. Onychophora— Class 3. 
Myriapoda— Class 4. Insecta (Hexapoda)— Type of Group— Lubber 
Grasshopper— Characteristics of More Important Races of Honey Bees 
—Methods of Insect Control— Class 5. Arachnida— Bibliography on 
Venomous Spiders— Other Classes— Xiphosura—Pycnogonida-Tardi- 
grada— General Consideration of the Arthropoda— Characteristics and 
Distribution— Integument and Musculature— Digestive System— 
Respiration— Circulatory System— Excretion— Nervous System and 
Sense Organs — Fossil Relatives. 

XIII— Chordata ^°9 

Classification— Sub-phylum Hemichorda (Enteropneusta)— Sub-phy- 
lum Urochorda (Tunicata)— Sub-phylum Cephalochorda (Adelochorda 
or Acrania)— Sub-phylum Vertebrata or Craniata— Class i. Cyclo- 
stomata— Class 2. Pisces— Class 3. Amphibia— Class 4. Reptilia— 
Class 5. Aves— Class 6. Mammalia— Invertebrates versus Verte- 
brates— Sub-phylum Hemichorda (Enteropneusta)— Type of Group— 
Balanoglossus— Sub-phylum Urochorda (Tunicata)— Sub-phylum 
Cephalochorda (Adelochorda or Acrania)— Type of Group— Amphi- 
oxus— Theories of the Origin of Vertebrates— Amphioxus— Arthropod 
—Annelid— Nemertean— Bibliography. 



221 



XIV — Cyclostomata 

Craniata— Classification— Characteristics— Cyclostomata— Character- 
istics — Myxinoids — Petromyzontia. 

XV— Pisces ^^"^ 

Classification— Characteristics— Natural History— Sub-class Elasmo- 
branchii— Type of Group— The Skate— Sub-class Teleostomi— Order I. 



X CONTENTS 

CHAPTER PAGE 

Crossopterygii — Order i. Chondrostei — Order 3. Holostei — Order 4. 
Teleostei — Sub-class Dipnoi — General Consideration of the Fishes — 
Locomotion — Coloration — Sound Producing Organs — Respiration — 
Poison Glands — Skin — Blood — Lymph — Endocrine Glands — Lymph- 
oid Tissue — Senses — Messmates and Associates — Parental Care — 
Habitat — ^Temperature — Electric Organs — Phosphorescent Organs — 
Adaptation of Fishes to their Environment — Economic Importance — 
Positive — Negative — Migration in Fishes — Homing Instinct — Fossil 
Relatives. 

XVI — Amphibia 265 

Classification — Apoda or Coecilians — Urodela or Caudata — Anura, 
Salientia or Ecaudata — Characteristics — Natural History — Order i. 
Apoda — Order 1. Urodela — Family i. Amphiumidae — Family 2. Sal- 
amandridae — Family 3. Oroteidae — Family 4. Sirenidae — Order 3. 
Anura — Family i. Pipidae, etc. — Family 2. Bufonidae — Family 3. 
Ranidae, etc. — Type of Group, Rana pipiens, the Leopard Frog — Ex- 
ternal Characters of the Frog — Skin — Muscle, Tendon, Fascia — Diges- 
tive System — Circulatory System — Action of the Heart — Respiratory 
System — Urinogenital System — Nervous System, Sense Organs — 
General Consideration of the Amphibia — Distribution — External Anat- 
omy — Skeleton — Muscles — Physiology — Digestive System — Respira- 
tory System — Circulatory System — Urinogenital System — Embryology 
— Parental Care — Parthenogenesis — Experimental Embryology — Re- 
generation — Habitat — Fossil Relatives — Economic Importance — Posi- 
tive — Poisonous Amphibians — Resistance of Amphibia to Poisons. 

XVII — Reptilia 302 

Amnion and Allantois — Classification — Characteristics — Natural His- 
tory — Super-order 2. Chelonia — Type of the Group — The Slider 
Terrapin — Super-order 6. Archosauria — Order Rhyncocephalia — Or- 
der Crocodilia — Order Squamata — Sub-order Lacertilia — Sub-order 
Ophidia — General Consideration of the Reptilia — Distribution — 
Anatomy and Locomotion — Digestive System — Respiratory System — 
Superficial Differences between the Crocodilia — Voice — Circulatory 
System — Excretory System — Reproductive System — Care of the Young 
— Nervous System and Sense Organs — Rattle of the Rattlesnake — 
Poisonous Reptiles — Action of Snake Venom on the Digestive Tract — 
Toxicity — Treatment of Snake Bite — Susceptibility of Snakes to Poison 
— Do Mother Snakes Swallow their Young? — Some Superstitions that 
Exist Regarding Snakes (Casselberry) — Fossil Relatives — Adapta- 
tions of Reptilia — References on Reptilia. 

XVIII— AvEs 334 

Division A. The Ratitae — Characteristics — Tinamous — Division B, 
The Carinatae — Characteristics — Classification — Order i. Pygopodes 
— Order 2. Longipennes — Order3. Tubinares — Order 4. Steganopodes 
— Order 5. Anseres — Order 6. Odontoglossae — Order 7. Herodiones — 



CONTENTS xi 

CHAPTER PAGE 

Order 8. Paludicolae — Order 9. Limicolae — Order 10. Gallinae — 
Order 11. Columbae — Order 12. Raptores — Order 13. Psittaci — Or- 
der 14. Coccyges — Order 15. Pici — Order 16. Machrochires — Order 
I. 17. Passeres — Natural History — -The Anatomy and Physiology of 

^ Birds — Characteristics — Temperature — Feathers — Color — Skeleton- 

Digestive System — Tongue — Buccal Glands — Esophagus — Crop — 
I Proventriculus— Gizzard — Small Intestine — Rectal Cecae — Rectum — 

Liver — Pancreas — Circulatory System — Respiratory System — Voice — 
Excretory System — Reproductive System — Nervous System — Sense 
Organs — Susceptibility of Birds to Poison — Types of Nests — Bird Mi- 
gration — Why Do Birds Migrate? — Speed of Flight — Economic Im- 
portance of Birds — Positive — Negative — Fossil Relatives — Arche- 
opteryx — Archeornis — Ichthyornis — Hesperornis — A Living Connect- 
ing Type. 

XIX — Natural History of Mammals 373 

Characteristics — Order i. Monotremata — Order 2. Marsupialia — 
Order 3. Insectivora — Order 4. Chiroptera — Order 5. Carnivora — 
Sub-order Fissipedia — Sub-order Pinnipedia — Order 6. Rodentia — 
Sub-order Simplicidentia — Sub-order Duplicidentia — Order 7. Eden- 
tata — Order 8. Ungulata — Sub-order Hyracoidea — Sub-order Peris- 
sodactyla — Sub-order Artiodactyla — Order 9. Sirenia — Order 10. Ce- 
tacea — Order 11. Primates — Races of Man — Fossil Man — Mam- 
mals as Migrants. 

XX — Mammalia — Physiology 420 

Man versus the Higher Apes — Physiology of the Vertebrate Animal — 
Mammalian Physiology — External Anatomy and Locomotion — His- 
tology — The Skin — Claws or Nails — Hair — Perspiration — Digestive 
System — Mouth — Teeth — Salivary Glands — Tongue— Esophagus — 
Stomach — Small Intestine — Liver — Pancreas — Digestion in the Small 
Intestine — Cecum — Appendix — Large Intestine — Digestion in the 
Ruminant — Chemical Characteristics of Protoplasm — Proteins — Col- 
loids — Precipitin Reaction — Carbohydrates — Monosaccharids — Disac- 
charids — Fats — Lipins — Chemical Elements of Protoplasm — Carbon — 
Hydrogen — Oxygen — Nitrogen — Mineral Salts — Sulphur — Phosphorus 
— Calcium — Silicon — Fluorine — Sodium — Chlorine — Potassium — 
Magnesium — Copper — Iodine — Arsenic — Iron — Manganese — Bro- 
mine — Boron — Zinc — Aluminium — Enzymes — Autocatalysts — Nutri- 
tion and Vitamins — The Organs of Internal Secretion — Endosecretory 
Glands vi'ith a Duct — Testis — Ovary — Liver — Pancreas — Ductless 
Glands — Thyroid — Parathyroid — Thymus — Suprarenal — Pineal — 
Pituitary — Interrelations of the Organs of Internal Secretion — Effects 
'* of Emotions on the Internal Secretions — References on the Endocrines 

— Circulatory System — Action of the Heart — Pulse — Comparative 
Anatomy of the Portal Systems— Blood — Blood Groups — Lymph — 
Lymphatics — Flow of Lymph — Spleen — Respiratory System — How 
Long Can Aquatic Mammals Submerge? — Voices of Mammals — Excre- 



xii CONTENTS 

CHAPTER PAGE 

tory System — Reproductive System — Female — Male — Propagation 
Rate in Mammals — Periods of Gestation — Nervous System and Sense 
Organs — A Triumph of Coordination — Fatigue in the Nerve Cell — 
Regeneration in the Nervous System — Hibernation and Aestivation 
Organs that Man Can Lose — Statistics of Vitality — Susceptibility 
of Mammals to Poison. 

XXI — Social Life of Animals 482 

Association of Different Species — Living Free — Commensalism — Sym- 
biosis — Parasitism — Effects of Parasitism — On Parasite — On Host — 
Association of the Same Species — Colonies — Communities — Gregari- 
ousness — Polygyny and Polyandry — Cases in which the Sexes Live 
Apart — Societies Composed of Different Species — Monogamy — Sea- 
sonal Mateships — Types of Families — Parent Families — Father 
Families — Mother Families — Child Families — References on Animal 
Relationships — Protection — Masking — Color Resemblance — Mimicry 
— Geographical Distribution— Barriers — Salinity of Water^ — Water 
Supply — Depth of Water — Temperature — Mountain Ranges — Do- 
mestication of Animals — Dog — Cat — Horse — Donkey — Pig — Cattle — 
Goat— Sheep — Rabbits — Pigeons— Fowls — Ducks — Geese — Peacocks 
— ^Turkeys — Tissue Survival Outside of the Body — Longevity of Ani- 
mals — Mammals — Birds — Reptiles — Amphibia — Fishes — Arthro- 
poda — MoUusca — Annelida — Coelenterata — Pulse Frequency. 

XXII — Evolution, Heredity, Eugenics 499 

Cell Division — Amitosis — Mitosis — Oogenesis — Spermatogenesis — Fer- 
tilization — Theories of Heredity and Evolution — History of the Evolu- 
tionary Idea — What we owe to Charles Darwin — Examples of Men- 
delian Inheritance in Man — The Origin of Species according to 
Lamarck, Darwin, Weismann, Mendel and DeVries — Evidences for 
the Theory of Evolution — i. Morphology — 2. Classification — 3. 
Blood Tests — 4. Embryology — 5. Paleontology — 6. Geographic Dis- 
tribution — Sex Determination — Sex Linked Characters — Crossing Over 
— Genes — Lethal Factors — Physiological Basis — Parthenogenesis — 
Identical versus Fraternal Twins — Hermaphroditism and the Free 
Martin — Hen Feathering in the Sebright Bantam — Evidence for and 
against the Inheritance of Acquired Characters — Inheritance of 
Disease — i. Prenatal Infection — 2. Prenatal Injury to the Germ Cells 
or Embryo — 3. Inheritance of Weakness Predisposing to Disease — 
4. Inheritance through the Germinal Substance — Maternal Impres- 
sions — Eugenics. 



CHAPTER I 



Introduction 






Living as they did near the Mediterranean and Aegean seas 
where tides receded and left animals upon the shore, and where 
insects developed in decayed flesh, it was natural that the early 
Greeks and Romans should believe in the spontaneous generation of 
life. This belief persisted until the experiments of an Italian 
naturalist, Redi, performed in 1688, showed that maggots originated 
in meat from eggs laid by flies. In the middle of the nineteenth 
century, Pasteur proved conclusively that not only larger organ- 
isms, but even minute bacteria would not develop in sterilized media 
unless they were introduced. 

We believe that all life came from pre-existing life — omne vivum 
ex vivo — but it is not our purpose to discuss in this text the various 
theories of how life came into being. • We are interested in the 
science of all living things, Biology (Gr. bios, life; logos, discourse), 
once termed Natural History, which includes the study of the struc- 
ture and activities of both plants and animals. While we must 
consider the plants in their relationship to animals, we cannot 
include the study of Botany, but must confine ourselves to the 
study of animals, called Zoology. 

The Function of Zoology.— The science of Zoology (Gr. zoon, 
animal; logos, discourse) indicates to us the relationship of animals 
from the unicellular to the most highly developed multicellular 
organism, man. In order to understand an animal thoroughly, we 
must know its anatomy, physiology, reaction to environmental 
conditions, and its economic importance. 

Medicine in all its aspects owes a great debt to Zoology, not only 
because of the opportunity to observe lower forms under favorable 
circumstances, but also because of the important relationship of 
parasitic animals to each other and to man. Some of the most 
important discoveries in sanitation and preventive medicme, as 
well as in surgery, have been made as a direct result of zoological 

studies. 

Agriculture owes much of its advancement to experimental work 



2 INTRODUCTION 

done by medical men and veterinarians, but within the past ten 
years physiologists and biochemists in agricultural and medical 
colleges have united in nutrition studies, undreamed in previous 
decades. 

The Divisions of Zoology. — Systematic Zoology, or Taxonomy 
(Gr. taxis, arrangement; nomas, law), has since the earliest days 
engaged the attention of naturalists. In fact, for many years they 
contented themselves with merely naming hundreds of animals. 
Fierce battles were waged over the question of priority and much 
time was wasted in futile arguments over species differences. In 
1735 a Swedish naturalist, who took the Latin name of Linnaeus, 
conceived the idea of a system of binomial nomenclature such that 
the generic and specific names written in Latin or Greek could be 
understood by scientists of all nations. Animals distinguished 
only slightly from each other were placed as different species of the 
same genus. For example, the domestic cat, the wild cat, and the 
lion belong to the same genus, which we call Felis; the domestic cat 
belongs to the species domestica and the lion is Felis leo. Over 

f 450,000 species of insects alone have been described. The branches 
of Systematic Zoology include, among others, CoTpe^^alogy, the clas- 
sification of Molluscs; Entomology, the classification of Insects; 
Herpetology, the classification of Reptiles; Ornithology, the classi- 
fication of Birds; and Mammalogy, the classification of Mammals. 
From comparison of external characters, science progressed to a 
study of internal arrangement and functions. Thus we have two 
great divisions arising, one which deals with the form and structure, 
being called Morphology (Gr. morphe, form; logos, discourse), and 
the other treating of the functions of organs and parts, called Physi- 
ology (Gr. phusis, nature; logos, discourse). 

Morphology includes Gross Anatomy (Gr. anatemno, to cut up), 
which deals with dissection; Histology (Gr. histos, a web; logos, 
discourse), which is the study of the structure of cells and tissues 
usually stained by dyes; Ejnbryology (Gr. en, in; bruo, bud), which 
traces the development of the egg; and Pathology (Gr. pathos, 
suffering; logos, discourse), which deals with the structure of diseased 
tissues. The study of Pathology is linked with Histology, Em- 
bryology and Physiology. 

But Zoology is by no means confined to the study of stained or 
preserved specimens. It is not the type of subject that it was 
termed by the Professor of Latin quoted by Conklin: "Biology 



INTRODUCTION 3 

deals with things as dead as the dead languages and not nearly as 
well preserved." 

Biology rests ultimately upon the foundation of the two funda- 
mental sciences, Physics and Chemistry. Recent advancement in 
the utilization of ultra-violet light and radium on animal growth 
gives us an inkling of the future possibilities in Physics. The com- 
paratively new science of Biochemistry is continually presenting us 
with explanations of extremely important physiological processes 
hitherto unknown. 

' In another age, all the branches of knowledge, whether relating to 
God, or man or nature, will become the knowledge of "the revelation 
of a single science," and all things, like the stars in heaven, will shed 
their light upon one another.' Jowett: Plato, Introduction to Meno. 

Physiology (Gr. phusisy nature; logos, discourse), the study of 
functions, includes the study of Animal Behavior and Psychology. 
Lovatt Evans, in an address before the British Association for the 
Advancement of Science, said: "Physiology is something more than 
bio-chemistry and bio-physics; it is and always will remain a bio- 
logical subject." 

Ecology (Gr. oikos, house; logos , discourse), the study of the re- 
lationship of animals to their environment, has developed far beyond 
the old Natural History of which Miall said: "Natural History 
is encumbered by multitudes of facts which are recorded only because 
they are easy to record." The study of Physiology is now so linked 
with that of Ecology that it is difficult to separate them. 

Zoogeography treats of the spatial distribution of animals while 
Paleozoology, which deals with their fossil remains, links Geology 
with Zoology. 

Evolution (Lat. e, out; volvere, roll), the study of the origin 
and descent (or ascent) of species, must draw upon all fields of 
Morphology and Physiology as well as on Taxonomy and Paleon- 
tology. Heredity treats of the transmission of characteristics from 
parents to offspring. Genetics deals with Heredity and Variation. 

Living Things Compared With Non-Living Matter. — The late 
Professor W. K. Brooks of Johns Hopkins University once said: 
"A living thing is a being which responds to the stimulus of any 
event in such a way as to adapt its actions to other events of which 
the stimulus is the sign." 

There are certain fundamental distinctions between living and 
non-living matter, as will be seen in the following table. 



INTRODUCTION 



Living and Non-Living Matter 



Each plant and animal has a definite size 
limit and form characteristic of the 
species. 

Living organisms grow by intussusception, 
the addition of particles of protoplasm 
prepared from their food by metabolic 
processes. 

Living organisms contain certain ele- 
ments characteristic of protoplasm, and 
Including complex proteins, built up from 
Carbon, Hydrogen, Oxygen and Nitro- 
gen, and undergo constant tearing down 
(katabolism) and upbuilding (anabo- 
llsm). 

Living organisms are able to reproduce 
complete Individuals like themselves, and 
to regenerate mutilated portions. 
Besides growth and reproduction, living 
matter has other powers: contractility, 
irritability, nutrition, respiration and ex- 
cretion. 



There is no limit to the size ^ or form 

reached by non-living matter (e.g. 

water). 

Non-living bodies grow by adding to 

themselves on the outside by accretion,^ 

accumulations of material chemically the 

same. 

Non-living matter may contain the same 

elements but be lacking In the spark of 

LIFE. 



Non-living matter Is utterly unable to 
reproduce. 

Non-living matter is devoid of these 
characteristics. 



Protoplasm 

Protoplasm is the term used to indicate that complex substance 
from which all living things are built up. Protoplasm is somewhat 
jelly-like in appearance, and nearly colorless, but may be opaque 
when it contains food particles. It is considered to be an emulsoid, 
existing either as an apparently liquid sol, with minute invisible 
molecules; or as a gel, firm in consistence, with larger visible par- 
ticles. Protoplasm is made up of "unit masses," which we term 
cells. Each cell has a nucleus and cytoplasm. Plant cells may 
have a cellulose wall, but in animal cells a cell wall is frequently 
absent. 

Structure of the Cell. — A cell is a complex living system or 
physiological unit of protoplasm which contains a nucleus. The 
protoplasm outside of the nucleus is usually called "cytoplasm." 
All the contents of the cell have been shown to be the seat of vital 
activity, but the nucleus contains certain elements, colored readily 
by dyes, hence called chromatin granules, which a vast amount of 

^ Since radiation pressure will in the end overcome gravity, even the mass of a star 
beginning as a nebula cannot exceed a certain limit. Nature abhors infinity of size. 
(J. A. Elesland.) 

^ Huxley cited crystals as an example of accretion. We now believe that crystals 
are assembled by electrical forces less complicated than in organic combinations. 



INTRODUCTION 



scientific study has shown to be the carriers of hereditary charac- 
teristics, but which may yet share the honors with unknown units. 
Chemical or physical agents may combine to determine the activity 
of these granules. 



Cey^fro/ bodies Coenfr-osomc) 



_ '^/" 

PJasmosome or true nucleolus f ■^Y_Mf-^'fc)te^.;,^^/(_' A 

Chromatin ^Z t^^W^^^M\'^^-A\ 

Linm _ ^ i-(^L-v<^P'_:.:c*--i^ 

Koryosome or chromatin- nucleoJus ' ' ^ ' 



vr/osom es 



:^^'^ I "-^ ,% V^V-'-Trive wall or membrane 

^^^m^^i^&i'V" ^'^■^■^'^^ i^etoplosmic or 

paroplosfic boc/i&s 

Fig. I. Diagram of a generalized cell. (After Wilson, The Cell in Development and 
Heredity. Courtesy of The Macmillan Co.) 

Cell Membrane and Cell Wall. — The cell membrane protects 
the cytoplasm from many physical and some chemical injuries. 
It is, however, only semi-permeable, and admits some solvents, but 
retains the colloids of its own protoplasm, and excludes foreign ones. 

On account of the tendency for water to pass or diffuse from a 
liquid with low concentration of soluble substance, through a per- 
meable membrane to a liquid with higher concentration, we find that 
the energy or osmotic pressure varies with the degree of similarity 
of the concentrations. In discussing two solutions, we refer to 
their tonicity. For example, a solution losing water through a 
membrane would be hypotonic, while the one that gained the water 
would be called hypertonic. Two solutions in osmotic equilibrium 
are called isotonic. 

The cell membrane may have a covering of some resistant 
material like chitin or hardened gelatin in the animals, or of woody 
cellulose in the plants. This covering is called the cell wall. 

Cytoplasm. — The most conspicuous structure in the cytoplasm, 
aside from the nucleus and certain large vesicles and plastids, is the 
centrosome, or central body (consult Figure i), which we find acting 
as the division center for the aster in mitotic division. (See page 
500.) No centrosome is present in the cells of flowering plants. 

Cytoplasmic Granules. — Granules of various kinds are scattered 
throughout the cytoplasm, suspended in the clear, viscid "hyalo- 
plasm." The relatively large yolk granules occur as solids, semi- 
solids or as liquid drops. Fat and glycogen appear as cell inclusions. 



6 INTRODUCTION 

Plastids, found chiefly in plant cells, aid in the formation of 
starch and various pigments. Chlorophyll bodies, the centers of 
formation of starch by photosynthesis, are considered the most 
important of the chloroplastic type. 

Secretory granules of various chemical composition and physical 
consistency, more or less transitory in nature, are found in secretory 
cells. They dissolve to produce fat, mucin, or an enzyme. (See 
page lo.) Storage granules are also quite generally distributed. 

Fibrillae, almost as characteristic as granules, appear in many 
types of cells, including gland cells, nerve cells and muscle cells. 
Fibrillae may be produced by the fusion of small granules, but like 
certain other cytoplasmic inclusions, some fibrillae are regarded as 
artifacts. 

The chondriosomes or mitochondria vary in form from granules 
of 0.2 mu. to rods and filaments of much greater length. They are 
found in most living cells and resemble albumins somewhat, both 
in solubility and in staining reactions. The earlier technique of 
fixation by acids such as acetic destroyed the mitochondria, but 
they are shown successfully in living cells by Janus Green B. 
Regaud suggested, as a possible explanation of their function, that 
they are the centers of chemical action, and that they extract 
substances from the protoplasm, transforming them into specific 
intra-cellular structures. Cowdry has suggested that they supply 
a surface-film, perhaps with a significance comparable to the nuclear 
and cytoplasmic membranes.^ 

The Golgi apparatus is the term given to a group of cell-com- 
ponents found widely distributed in both plant and animal cells. 
They, like chondriosomes, require fixation by reagents lacking 
acetic acid. Osmic acid fixers seem to show them best. The 
apparatus appears in diffuse form as separate bodies, or in localized 
form as a "Golgi net" consisting of concentrated fibrils. It has 
been suggested by Nassanov, Bowen and others that the Golgi- 
bodies have a secretory function. Bowen suggested that the Golgi 
apparatus may be a center for the formation of enzymes. 

H. Hibbard (Arch. d'BioL, Tom. 38, p. i, 1927) and M. Parat 
(Arch. d'Anat. mic, Tom. 24, p. 73, 1928) have shown that Golgi- 
bodies may be depositions of the stain used. We are still in con- 
siderable doubt regarding the function of Golgi-bodies, mitochon- 

' Consult Osterhout, W. J. V. 1929. Some aspects of permeability and bioelec- 
trical phenomena. Bull. Nat. Res. Council, pp. 170-288, Washington, D. C. 



INTRODUCTION 7 

dria and other cell components, but it Is hoped that improved tech- 
nique in fixation and staining, together with the development of 
tissue culture studies and the micro-manipulation of living cells, 
will reveal the functions of real structures and indicate which 
granules are only artifacts. 

There are other scattered bodies in the cytoplasm, not readily 
seen but "haloed" under strong illumination, which may be the 
ultimate units from which chondriosomes and Golgi-bodies are 
aggregated. 

Nucleus. — The nucleus is visible in living cells. Some cells 
contain several nuclei, as in the giant cells of bone marrow, and 
many others are found to contain two types of nuclei, certain 
protozoa, In fact, having both a nutritive and a reproductive 
nucleus. The nucleus is essential to the life of the cell, and is related 
to metabolism and the secretory phenomena. 

The nuclear monbrane, tough and elastic. Is found In the majority 
of animal cells, but is absent in certain protozoa. It disappears 
during mitosis (indirect cell division, page 500). 

The nucleo-reticulum consists of chromatin, which Is stained by 
basic dyes. Chromatin may appear in the form of fine granules, 
larger granules, or in a network, with net-knots of massed granules. 
(See Fig. i.) 

Chromatin granules {chromomereSy chromioles) are suspended on 
a reticulum of linin, which is delicate In structure and stained by 
acid dyes. The granules aggregate to form chromosomes,'* which 
are constant In number for the cells of the same species. Appar- 
ently the granules are not dissociated, but usually prepared to 
reassemble. The chromosomes are carriers of hereditary /«f/orj or 
"genes," although we are not certain that they are the sole means of 
transmission from one generation to the next. (See p. 538.) 

Nucleolus. — The nucleolus or plasmosome Is a dense body, 
spherical in shape, and chemically different from chromatin since 
it Is stained with acid dyes. During cell division, the nucleolus 
usually disappears. Sometimes there are several nucleoli, which 
may play a part in the metabolism of the cell. 

Structure of Protoplasm. — The fact that protoplasm differs 
under various physiological conditions has given rise to several 

*" Chromosomes are individual chromatic elements which appear definitely in 
the nucleus at the end of the prophase stage and which act as unit structures during 
mitosis." E. Carothers. See page 500 for a discussion of mitosis. 



8 INTRODUCTION 

theories of its structure. The granular theory suggests that a 
protoplasmic mass is made up of minute granules which mass into 
solids or arrange themselves in a linear series to form fibrils. The 
fibrillar theory notes the fibrous structure of certain organs and 
stresses the idea of a feltwork of fibrils. According to the reticular 
theory, protoplasm is to be compared to a fish net or a hammock. 
The alveolar theory indicates that protoplasm is comparable to an 
emulsion such as milk, or a mixture of oil and water. The colloidal 
theory recently championed by E. B. Wilson suggests that the alveoli 
are of secondary origin and that the ultimate particles, "minute 
scattered bodies, finally produce an emulsion-like structure." 

Physiological Properties. — Protoplasm has the power to utilize 
foods, to grow and repair wastes and develop energy. It secretes 
usable material and excretes wastes. Repair of broken-down tissues 
and construction of new is termed anabolism. The destruction of 
waste materials is called katabolism. Both processes combined, 
which result in life activity, are called 7netabolism. Protoplasm 
responds to all sorts of external stimuli, adjusting itself to the 
environment whenever possible. Finally it has the power of re- 
production and a limited power of regeneration. 

Chemical Composition. — When we attempt an analysis of the 
chemical constituents of living protoplasm, we induce important 
changes. By weighing the material before treating it, and then com- 
paring the weights of all substances determined, we find that it is 
possible to learn most of the constituents, except that all important 
one — LIFE. Protoplasm consists of proteins, carbohydrates, fats, 
inorganic salts, enzymes, water and the "vitamins." 

Proteins, which constitute about 40 per cent of dry protoplasm, 
are compounds with high molecular weights, containing about 53 
per cent carbon, 22 per cent oxygen, 17 per cent nitrogen, 7 per cent 
hydrogen. They also contain small quantities of sulphur and 
phosphorus. Proteins include the albumen of eggs, fibrin of the 
blood and casein of milk. They are colloids, and as such do not 
readily diffuse through membranes nor go into solution. 

Carbohydrates, which constitute about 11 per cent of dry pro- 
toplasm, consist of carbon, hydrogen and oxygen, the last two 
elements being always present in the same ratio as in water, dextrose 
for example being C6H12O6. Glycogen, the only example of animal 
starch, is found chiefly in the liver and muscles. Carbohydrates 
can be converted into fats. 



INTRODUCTION 9 

Fats, constituting about 12 per cent of dry protoplasm, contain 
carbon, hydrogen, and oxygen in such proportions that there is 
much less oxygen than in the carbohydrates. Fats of the body are 
derived from fatty substances consumed and are also formed from 
carbohydrates and proteins. Fats are essential in maintaining the 
proper body temperature. 

Water is most essential to life and constitutes over 50 per cent 
of the weight of most animals. Even the most ardent anti-pro- 
hibitionist is made up of about 60 per cent water. It is necessary 
to bathe tissues and to furnish the adequate liquid for blood, lymph 
and cerebro-spinal fluid. 

Chemical Elements of Protoplasm. — Carbon compounds are the 
primary materials of protoplasm. About 18 per cent of protoplasm 
consists of carbon. Carbon unites with oxygen to form carbon 
dioxide |B|HflH| and to liberate energy. 

Hyaroger^^hout 1 1 per cent of protoplasm) is taken into the 
bodies of plants and animals in combination with oxygen as water, 
and is also excreted in this form. 

Oxygen is found in the free state and unites with various com- 
pounds of protoplasm, the process of oxidation releasing energy. 
In combination with living tissues we find that oxygen makes up 
about 65 per cent of protoplasm. 

Nitrogen is essential to protoplasm of which it comprises about 
1 per cent. It forms 79 per cent of the atmosphere. Taken into 
plant bodies usually in the form of nitrates, the plants utilize it in 
the manufacture of proteins. Jfjimonia, a nitrogen compound, 
formed in the katabolism of plants and animals, is changed by 
certain bacteria into nitrates which are then absorbed by plants. 

Sulphur, usually found in the soil as calcium sulphate, is ab- 
sorbed by plants and used in the manufacture of some amino-acids. 

Mineral Salts, Enzymes, Hormones and Vitamins. — The above 
elements are said to comprise about 99 per cent of the weight of an 
animal, but there are a number of other elements present in various 
chemical combinations in extremely minute quantities. Some of 
these are absolutely necessary to life, while others influence the 
glands of internal secretion and thus aflfect growth. Among the 
most important of these elements are iodine, iron, calcium, phos- 
phorus, chlorine, magnesium, potassium, and sodium. Other 
elements assuming greater importance every day are arsenic, 
manganese, copper and zinc. Suffice it to say here that mineral 



10 INTRODUCTION 

salts are so essential to life that if they are withheld from the 
animal body, death ensues much more quickly than from the lack 
of proteins, carbohydrates, and fats. In solution the salts of the 
body provide the proper medium for living tissues, and aid in main- 
taining the optimum condition of physiological equilibrium. (For 
a further discussion of the significance of the salts of these elements 
see page 437.) 

Enzymes are complex organic substances produced in living cells 
by glands some of which are modified to produce other important 
secretions. Enzymes are able as catalysts to hasten chemical reac- 
tions, but do not enter into the end product of the reaction, and are 
not themselves consumed. 

Endocrine glands are glands of internal secretion that produce 
catalyzing hormones which act as "messengers of stimulation," in- 
fluence growth, and regulate the animal througlfHlyMjj^ole life. 
(See page 444.) 

Vitamins are certain accessory food factors that have been 
studied extensively since 191 1. Just what their chemical com- 
position may be has not yet been fully decided. The reader will 
find further discussion of the subject in the section on Nutrition and 
the Endocrines (page 441). 

Animal Relationships 

Fitness to Survive. — If we study simply the structure and the 
activities of organisms and neglect the relation of the living being 
to its environment, our study is not Biology, or the science of life. 
Biology introduces a new problem, that of fitness. Biology asks 
"When, how, why.?" Aristotle said: "The essence of a living thing 
is not what it is made of, nor what it does, but why it does it." 

It is the adjustment of the individual to his environment which 
makes life possible. Life is one long continuous fight, a "struggle 
for existence." T. R. Malthus in his "Principles of Population" 
showed that human population tends to increase in a geometrical 
ratio (i, 2, 4, 8) while the food supply tends to increase in an arith- 
metical ratio (i, 2, 3, 4, 5, 6, 7, 8). Famines are still occurring in 
India and China. 

Today man is dependent on his fellow man for his subsistence 
and directly or indirectly dependent on the plants and animals 
about him. Each animal or plant represents a force in Nature and 
is beneficial or injurious. If we study the habits of animals we will 



INTRODUCTION ii 

be able to evaluate them and to determine whether they should be 
treated as friends and encouraged to increase, or even artificially- 
propagated, or whether they should be attacked by chemical and 
mechanical agencies or by protecting their natural enemies. 

The most practical way within our reach of studying that 
adjustment between the organism and the external world — the 
fitness — which constitutes life is to learn all we can about the 
physical basis, and all we can about its fitness. 

To study life, we must consider three things: (i) the orderly 
sequence of external nature; (2) the living organism and the changes 
that take place in it; and (3) that continuous adjustment between 
the two sets of phenomena which constitutes life. 

Plants and Animals. — It might appear that, since man is an 
animal, Zoology is the more important of the two studies. But we 
must remember our thesis — the proper relation of the individual to 
his environment — and we will see that plants and animals alike make 
up the environment. The study of the relation of animals and 
plants to disease is at present demanding the attention of some 
of the world's greatest scientists. 

To Linnaeus (1707-78) we owe the classification of plants and 
animals. He stated that "plants grow and live, while animals 
grow, live, and feed." Owen (1803-93) declared that a definition 
of plants excluding all animals, or of animals excluding all plants, 
is impossible. As we go down to the simplest forms we find dif- 
ficulty in distinguishing between plant and animal. No one can 
tell. We call these lowest types Zoophytes (Protista) and Phytozoa. 

Origin. — Every organism kiiown in nature arises as a simple cell. 
In the plant we call it the ovule; in the animal the ovum. 

Composition. — So far as their chemical nature is concerned, the 
plant and animal cell are the same. This has been repeatedly 
proved. All contain carbon, hydrogen, oxygen, and nitrogen. 
The skeletons, however, differ widely. The skeleton is largely a 
cell wall modified in many ways. In general, plants exhibit a linear 
aggregation of cells, while animals show a mass aggregation. 

Morphology. — No outline can be drawn which will be common 
to all plants and animals. 

Physiology. — Plants and animals stand widest apart in the 
mode of nutrition, and here we have the chief distinctions: 



12 



INTRODUCTION 



Characteristics of /inimals 

Animals usually have a 
definite shape and are 
possessed of automatic 
motion. 

Animals depend chiefly on 
solid food which is liqui- 
fied by internal digestion. 

Animals derive carbon 
from starch, sugars, fats, 
from plants and from 
other animals. 

Animals derive their Ni- 
trogen from complex ni- 
trogenous compounds 
formed by other organ- 
isms. They secrete Ni- 
trogenous wastes. 

Animals are chiefly de- 
void of chlorophyll. 



Animals are composed of 
cells with or without cell 
walls and chiefly without 
cellulose. 

Animals have more 
marked division of labor 
among the organs and tis- 
sues of the body. 

Animals use the potential 
energy of food, changing 
it into kinetic energy. 
We may say they are 
generally oxidizers. 



Animals are destructive 
or katabolic. 



Exceptions 

Some plants move and 
some animals are sta- 
tionary. 

Certain parasites, animal 
and plant, absorb food 
from that to which they 
are attached. 

Symbiotes in hydra make 
food for hydra and hydra 
makes CO2 for symbiotes. 
Fungi are also exceptions. 

Some Protozoa live like 
plants and some plants 
are carnivorous. 



Some protozoa, sponges 
and coelenterates have 
chlorophyll while some 
parasitic plants have no 
chlorophyll. 

Cellulose is found In 
Flagellates and the tunic 
of Tunicates. 



Characteristics of Plants 

Plants have a more vari- 
able shape and are devoid 
of automatic motion. 

Plants absorb food In the 
form of liquid or gases. 



Plants derive their Car- 
bon chiefly from CO2 of 
the air and water. 

Plants derive their Nitro- 
gen from simple Nitrogen 
compounds especially in 
the soil. They do not 
give oflF Nitrogenous 
wastes. 

Plants are chiefly chloro- 
phyll bearing and use the 
kinetic energy of sunlight 
in building up complex 
compounds. 

Plants are composed of 
cells with definite cellu- 
lose walls 

Plant cells show little 
division of labor. 



Plants build up simple 
food into complex sub- 
stances. They convert 
kinetic energy of sunlight 
into potential chemcal 
energy. They are re- 
ducers of carbon dioxide, 
liberating oxygen. 

Plants are predominantly 
constructive or anabolic. 
They make more energy 
than they can use. 



Classification 

Natural Classification is an attempt to group animals on the 
basis of similarity in structure and probable relationship. 



INTRODUCTION 13 

Let us trace the cat from Kingdom to Species. 

Kingdom — Animalia 
Phylum — Ch or data 

Su b-Ph YLUM — Vertebrata 
Class — Mammalia 
Order — Carnivora 
Fami l y — Felidae 
Genus — Felis 

Species — Felis domestica. 

Metazoa. — /\nimals belonging to the Phyla above the Protozoa 
have many cells and are called Metazoa (Gr. meta, beyond; zoow, 
animal). Beginning as single cells, the Metazoa pass through 
stages in which the cells are arranged in at least two layers, the 
ectoderm and the endoderm. As adults Metazoa are made up of 
cells arranged in unlike groups. Definitely specialized for par- 
ticular functions, we find the cells dependent on one another, and 
manifesting a pronounced "division of labor." 

It is customary to begin the study of zoology with types of the 
Protozoa, the lowest of the great divisions of animals. But before 
we take up these forms, it may be well to survey briefly the animal 
kingdom, beginning with the highest group of Vertebrates, the 
Mammalia, to which class we belong. 

Vertebrates 

Vertebrates belong to the most highly developed Phylum of the 
animal kingdom, called Chordata. Members of this group include 
five well known classes, Fishes, Amphibians, Reptiles, Birds, and 
Mammals. All of them possess a bony axis called the backbone or 
vertebral column. In general we find that the vertebrates are of 
much larger size than the invertebrates, and their greater activity 
is accompanied by special adaptations of structure. 

Phylum — Chordata. — 

Sub-Phylum — Vertebrata 

Class I. Cyclostomata 

Class II. Pisces 

Class III. Amphibia 

Class IV. Reptllia 

Class V. Aves 

Class VI. Mammalia 



14 INTRODUCTION 

To the vertebrates belong all the most familiar animals such as 
fishes, frogs, snakes and dogs. Vertebrates have certain structures 
in common: 

I. Remarkable similarity in the three divisions of the body, 
head, trunk, and tail. 

1. All vertebrates are bilaterally symmetrical, i.e. a plane passed 
through an axis of the body will divide it into two equal halves. 

3. A supporting axis, the notochord, is found at some stage of 
development in all forms, but is replaced in all higher vertebrates 
by an axial skeleton. Both appendicular and axial skeleton are 
internal. 

4. All vertebrates have two body cavities, the coelom and the 
digestive tube. 

5. The nerve cord is hollow and dorsal to the alimentary canal. 

Class Mammalia (13,000 species). — Mammals are warm-blooded 
animals with hair or wool covering the body, having a muscular 
diaphragm which separates the chest from the abdomen. They 
never have gills, but breathe by lungs. They have a well developed 
and usually convoluted brain with many important association 
tracts. While some mammals are adapted to aquatic and others 
to aerial life, the majority are suited to life on land. Except in a 
few of the lower forms we find that before birth young mammals 
are closely attached to their mothers by a structure called the 
placenta. In general, mammals are further advanced at birth than 
in the lower classes of vertebrates. Mammary glands furnish 
nourishment to the young until they are able to shift for them- 
selves. Mammals range from the most highly developed form, 
man, to the primitive duckbill platypus, which lays eggs and has 
diffuse mammary glands. 

Class Aves (23,000 species). — Birds are unlike mammals, having 
specialized in a quite different direction. They have a body tem- 
perature ten degrees higher than that of the mammals, and are dis- 
tinguished from all other animals by the presence of feathers. Their 
highly developed wings and pectoral muscles, hollow bones, large 
lungs, and air sacs adapt the majority of them to an aerial life, 
although some forms like the ostrich are flightless. Birds are of 
great economic importance in the extermination of insects, but they 
are of aesthetic value since many of them are beautifully colored, 
while others are sweet singers. 

Class Reptilia (5,000 species). — Reptiles differ more widely 



INTRODUCTION 



15 



among themselves than other classes of vertebrates. In some 
respects they appear to be related to both birds and mammals. 
They have scaly or armored skins, never have gills, but breathe by 
lungs and are cold blooded. They have three chambers to the 
heart, the ventricular septum being perforate in all except the 
crocodilia. Living forms are terrestrial or aquatic but extinct forms 
were aerial. With the exception of a few lizards and snakes, they 
are oviparous. (Lizards, snakes, turtles, alligators.) 

Class Amphibia (4,000 species). — With slimy skins, the modern 
species lacking armor, but externally resembling the reptiles so 
much that Cuvier once termed them "naked reptiles," the amphibia 
mark a transition from the aquatic life of fishes to the terrestrial 
life of reptiles. In the larval condition practically all amphibia 
have gills, while as adults they breathe by lungs, although in some 
forms gills still persist. Amphibia are cold blooded, and their 
unpaired fins are never supported by fin rays. They are, with a few 
exceptions, oviparous. (Salamanders, frogs, toads.) 

Class Pisces (20,000 species). — As strikingly adapted to life in 
the water as birds are to life in the air, the fishes are all aquatic, 
moving chiefly by a muscular tail. They have paired appendages 
in the form of fins, and unpaired median fins always supported by 
fin rays. All have permanent gills supported by cartilaginous or 
bony gill arches. Fishes are cold blooded, the body temperature 
remaining the same as that of the medium in which they swim. 
The heart is two chambered, only the lung fishes exhibiting a prim- 
itive auricular septum. In the skin of most fishes, one finds scales. 
Some fishes are oviparous, others are viviparous. (Shark, sturgeon, 
mackerel, trout.) 

Class Cyclostomata. — While they somewhat resemble the bony 
true eels, the hags and lampreys have no jaws, no lateral appendages 
and no scales. A rasping tongue and a circular sucking mouth are 
present. The gills are pocket-like and the vertebrae are separate 
from the notochord. Lampreys are true vertebrate parasites. 

Sub-phylum Adelochorda {Cephalochordd). — Fish-like forms once 
classed with the mollusca. Branchiostoma (Amphioxus) has a 
dorsal fin, lateral metapleural folds, well developed myotomes, and 
a persistent notochord. The nerve cord has a neurocele. A 
pharynx, with many gill slits, leads into a ventral atrium and 
currents pass out the atriopore. A cranium is absent. 

Sub-phylum Urochorda (1,500 species). — Once called worms, the 



i6 INTRODUCTION 

tunicates or "sea squirts" were later called mollusca. They are 
characterized by a cellulose tunic, retrogressive metamorphosis 
and reversible heart beat. 

Invertebrates 

Having described briefly the Urochorda and Adelochorda, which 
we may consider types intermediate between the Vertebrates and 
the Invertebrates, let us consider the characteristics that differen- 
tiate the Invertebrate Phyla. We have seen that all the Verte- 
brates belong to the same Phylum, and are to a great extent related, 
but the Invertebrate Phyla are widely different in characteristics. 

1. Invertebrates have neither internal skeleton nor notochord. 

2. For the most part their nervous system is ventral to the di- 
gestive tract. 

3. They lack gill slits or visceral clefts. 

4. When present, the heart is dorsal. 

Phylum Arthropoda (450,000 species). — Segmented animals, 
some with jointed appendages. Body covered by a chitinous exo- 
skeleton secreted by cells beneath It; bilaterally symmetrical, with 
anus but poorly developed coelom. (Examples — crab, spider, mos- 
quito.) 

Phylum Mollusca (60,000 species). — Unsegmented with no true 
appendages. Fundamental bilateral symmetry Is lost in Gastro- 
poda; while the ventral muscular foot characteristic of the group is 
subject to modification. Frequently a bilobed shell is present with 
the mantle, a dorsal fold of the body wall covering the animal. 
Sometimes both shell and mantle are absent; but a coelom and anus 
are present. (Examples — oyster, clam, snail and octopus.) 

Phylum Molluscoidea (2,000 species). — a. Bryozoa or Polyzoa- 
Colonlal, like some Coelenterates. Complete alimentary canal. 
Large body cavity. (Pectinatella is the commonest fresh water 
form.) b. Brachiopoda — once gigantic bivalves, rulers of the ocean. 

Phylum Trochelminthes (500 species). — Somewhat resembling 
the Infusorian protozoa, the Rotifers are often called "wheel ani- 
malcules." Well developed digestive system with mouth, mastax 
(chewing stomach), glandular stomach, intestine and anus. Fe- 
males large, males few In number and small; resemble larvae of 
annelids and molluscs. 

Phylum Annelida (4,000 species). — Visibly segmented worms 
with three cellular layers. (Triploblastic.) No jointed appen- 



INTRODUCTION 17 

dages; setae in the skin. Coelom opens to exterior by dorsal pores 
and ventral nephridiopores. Alimentary canal well developed and 
usually specialized. Nervous system consists of two dorsal ganglia 
and a ventral chain of ganglia. (Examples — earthworm, leech.) 

Phylum Echinodermata (3,000 species). — Triploblastic (three 
layered) with a calcareous exoskeleton in plates or as spicules; 
larvae bilaterally symmetrical but adults radially symmetrical. 
The coelom is well developed; slow locomotion facilitated by water 
vascular system; all marine; never bud to form a colony. (Ex- 
amples — starfish, sea urchin, and brittle star.) 

Phylum Nemathelminthes (1,500 species). — Unsegmented with 
an elongate cylindrical body covered with tough cuticle; tubular 
digestive tract with mouth and anus; coelom present; paired ex- 
cretory organs and tubular gonads; nerve ring and associated gan- 
glia; many parasitic. (Examples — hookworm, eel-worm, trichina.) 

Phylum Platyhelminthes (4,600 species). — Unsegmented flat- 
tened worms, bilaterally symmetrical and with three distinct layers 
(triploblastic). Free living forms have a gastro-vascular cavity 
with no anus, while the degenerate parasitic forms lack a digestive 
cavity. (Examples — liver fluke, tape worm, and planaria.) 

Phylum Coelenterata (4,500 species). — Radially symmetrical 
with two cellular layers, and a non-cellular mesoglea; single gastro- 
vascular cavity or Coelenteron; formerly called Zoophytes. Sting- 
ing cells or nematocysts in the body wall. (Examples — corals, sea 
anemones, jelly fishes and hydroids.) 

Phylum Porifera (2,500 species). — Bodies of sponges consist 
of a mass of connective tissue with two-layered (diploblastic) body 
wall penetrated by canals or pores. All are aquatic, mostly marine. 
Radially symmetrical; skeleton of spicules usually supports the body 
wall. (The common bath sponge is an example.) 

Phylum Protozoa (10,000 species). — Although it would seem 
that in some respects sponges might be considered colonial Protozoa, 
we must distinguish the latter from all Metazoa by their charac- 
teristic of being complete single celled animals, without true tissues. 
They are mostly so small as to be visible only with the aid of a 
microscope; many species are colonial; many are parasitic. 

PHYLUM PROTOZOA. 
Class I. Sarcodina. 
Class II. Mastigophora 
Class III. Infusoria. 
Class IV. Sporozoa. 



1 8 INTRODUCTION 



PHYLUM PORIFERA. 

PHYLUM COELENTERATA. 
Class L Hydrozoa. 
Class n. Scyphozoa. 
Class IIL Actinozoa or Anthozoa. 

PHYLUM OR CLASS CTENOPHORA. 

PHYLUM PLATYHELMINTHES. 
Class L Turbellaria. 
Class IL Trematoda. 
Class IIL Cestoda. 
Uncertain Class, Nemertinea. 

PHYLUM NEMATHELMINTHES. 
Class I. Nematoda. 
Uncertain Classes. 
Acanthocephala. 
Gordiaceae. 

PHYLUM ANNULATA, OR ANNELIDA. 
Class I. Archi-Annelida. 
Class II. Chaetopoda. 
Class III. Hirudinea. 

PHYLUM TROCHELMINTHES. 

PHYLUM MOLLUSCOIDEA. 
Class I. Brachiopoda. 
Class IL Bryozoa. 
Class IIL Phoronidea. 

PHYLUM ECHINODERMATA. 
Class I. Asteroidea. 
Class II. Ophiuroidea. 
^^}\ Class III. Echiftoidea. 

Class IV. Holothuroldea. 

PHYLUM MOLLUSCA. 
Class I. Pelecypoda. 
Class IL Amphineura. 
Class III. Gastropoda. 
Class IV. Scaphopoda. 
Class V. Cephalopoda. 

PHYLUM ARTHROPODA. 
Class I. Crustacea. 
Class II. Onychophora. 
Class III. Myriapoda. 
Class IV. Insecta (Hexapoda). 

Order i. Thysanura (Aptera). 

Order 2. Ephemerida. 

Order 3. Odonata. 

Order 4. Plecoptera. 

Order 5. Isoptera. 

Order 6. Corrodentia. 



INTRODUCTION 19 



Order 7. Mallophaga. 

Order 8. Thysanoptera. 

Order 9. Euplexoptera. 
Order 10. Orthoptera. 
Order 11. Hemiptera. 
Order 12. Neuroptera. 
Order 13. Mecoptera. 
Order I4. Trichoptera. 
Order 15. Lepidoptera. 
Order 16. Diptera. 
Order 17. Siphonaptera. 
Order 18. Coleoptera. 
Order 19. Hymenoptera. 

Class V. Arachnida. 

Other Classes. 

Pycnogonida. 
Tardigrada, 

PHYLUM CHORDATA. 

Sub-phylum Hemichorda (Enteropneusta). 
Sub-phylum Urochorda (Tunicata). 
Sub-phylum Cephalochorda (Adelochorda or Acrania). 
Sub-phylum Vertebrata or Craniata. 

Class I. Cyclostomata, 

Class II. Pisces. 

Sub-class Elasmobranchii. 
Sub-class Teleostomi. 

Order i. Crossopterygii. 

Order 2. Chondrostei. 

Order 3. Holostei. 

Order 4. Teleostei. 
Sub-class Dipnoi. 

Class III. Amphibia. 

Order i. Apoda or Coecilians. 
Order 2. Urodela or Caudata. 
Order 3. Anura (Salientia or Ecaudata). 

Class IV. Reptilia. 

Super-order i. Cotylosauria. 

Super-order 2. Chelonia. 

Super-order 3. Therapsida (Theromorpha). 

Super-order 4. Sauropterygia. 

Super-order 5. Ichthyopterygia. 

Super-order 6. Archosauria. 

Class V. Aves. 

Division A. Ratitae. 
Division B. Carinatae. 

Order i. Pygopodes. 

Order 2. Longipennes. 

Order 3. Tubinares. 



20 INTRODUCTION 

Order 4. Steganopodes. 
Order 5. Anseres. 
Order 6. Odontoglossae. 
Order 7. Herodiones. 
Order 8. Paludicolae. 
Order 9. Limicolae. 
Order 10. Gallinae. 
Order 11. Columbae. 
Order 12. Raptores. 
Order 13. Psittaci. 
Order 14. Coccyges. 
Order 15. Pici. 
Order 16. Machrochires. 
Order 17. Passeres. 

Class VI. Mammalia. 

Order i. Monotremata. 
Order 2. Marsupialia. 
Order 3. Insectivora. 
Order 4. Chiroptera. 
Order 5. Carnivora. 

Sub-order Fissipedia. 

Sub-order Pinnipedia. 
Order 6. Rodentia. 

Sub-order Simplicidentia. 

Sub-order Duplicidentia. 
Order 7. Edentata. 
Order 8. Ungulata. 

Sub-order Hyracoidea. 

Sub-order Perissodactyla. 

Sub order Artiodactyla. 
Order 9. Sirenia. 
Order 10. Cetacea. 
Order 11. Primates. 



CHAPTER II 



Protozoa 



The Protozoa (Gr. protos, first; zoon, animal) are the simplest 
living animals and some of them resemble plants. Primitive and 
mostly microscopic though they are, the Protozoa are complete 
organisms in a single cell, carrying on the physiological processes of 
higher forms. A protozoan may be ameboid, flagellated, or ciliated, 
depending on its organs of locomotion. 

Classification 

Class 1. Sarcodina (Gr. sarx, flesh) move by false feet or pseudo- 
podia. 

Class 2. Mastigophora (Gr. ?nasfix, whip; and phero, bear) move by 
flagella. 

Class 3. Infusoria (Lat. in/usus, crowd In) move by cilia, and are 
also called Ciliata. 

Class 4. Sporozoa (Gr. spo?'a, seed; and zoon, animal). No loco- 
motor organs in adult stage. 

Characteristics 

1. Morphologically the simplest ones are equal to isolated epi- 

thelium. 

2. Physiologically they are equal to the whole group of cells making 

up the human body. Protozoa are complete unicellular 
organisms and many have a brief multicellular phase. 

3. Functionally they epitomize life processes. 

4. Theoretically they are generalized cells. 

5. Of practical economic importance, they cause many diseases. 

6. As soil organisms protozoa are of doubtful importance. 

Protozoa were first discovered by Leeuwenhoek in rain water. 
Misconceptions arose because of the insufficient magnification 
possible. O. F. Mueller (1786) made the first classification. He 
classified 350 species, 150 of which are still regarded as valid. He 

21 



22 



PROTOZOA 



believed them to be the simplest form of animal. Von Siebold and 
Kolliker (1849) proved that Protozoa are single cells and complete 
organisms as well. Max Schultze (1865) gave the present idea. 

Natural History 

Class I. Sarcodina. Type of Group — Ameha proteus. Ex- 
terna/ Anatomy. — Amebae resemble minute grayish animated par- 
ticles of jelly. Some species of amebae, large enough to be seen 



Pseudopodium 





Cry:sfal 

4^ ii^fe^"'^^^'^ 



' •S:'a 



vacuole V . -fiT^ - ^^■■&-'-^^^^^=^- — -^^r—Food particle 






Fig. iA. Ameba proteus-dubia SchaefFer. (Drawn by H. N. Lammers, after E. F. 
Botsford, Jour. Exp. Zool., vols. 45-46, 1927.) 

with the naked eye, have been selected and cultivated for laboratory 
use. The diameter of the smaller ones is as little as five microns. 
They constantly change their shape, sending out little projections 
called pseudopodia, or "false feet" (Fig. 2, A and B). 

The outer covering of the ameba is called the ectosarc (ectoplasm) 
and is lacking in color. The inner portion of the animal called the 
endosarc (endoplasm) contains the nucleus, the synthetic and 
hereditary center of life, and vacuoles of different types. The 



PROTOZOA 



23 



presence of numerous granules and particles of food gives the 
animal a grayish appearance. 






Fig. iB. Jmeia dividing. (Drawn by H. N. Lammers, after E. F. Botsford, Jour. 

Exp. Zool., vols. 45-46, 1927.) 

Locomotion. — There are a number of theories attempting to 
explain the movement of ameba, but none of them seems quite 
adequate. 

According to the contractile theory of Bellinger (1906) and others, 
contractile fibrillae were postulated. He showed that when viewed 
with the microscope in a horizontal position the ameba "walks" 
on stiff pseudopodia ^ (Fig. 3 A). 



is-iiri 







\~-AdvQncinq pseudopodium 



Fig. 3//. Locomotion of Ameba. (After Bellinger.) 

The surface tension theory indicates that ectoplasm is most 
rapidly formed at the point where surface tension is increased. 
Schaeffer (1920) has also emphasized the fact that ameba has a 
wavy path or a flattened spiral.^ 

The adherence theory states that a pseudopodium adheres more 
strongly to one side and that the endoplasm of that region, and 
ultimately the whole animal, moves in that direction. 

In the theory advanced by Mast (1923) ^ it is suggested that 

1 Dellinger, O. P. 1906. Locomotion of Ameba and allied forms. Jour. Exp. 
Z06I., vol. 13, pp. 337-358. 

2 Schaeffer, A. A. 1920. Ameboid Movement. Princeton University Press. 

^ Mast, S. O. 1923. Mechanics of locomotion in Ameba. Proc. Nat. Acad. 
Sci., vol. 9, pp. 258-261. 



24 



PROTOZOA 



Shell, composed of sond 




Fig. 35. 



Pseud o podia 

Difflugia. (After Leidy.) 



the moveme'tit of ameba is dependent on changes of the protoplasm 
from sol to gel and back to a sol state again. (See page 4.) It 
has also been suggested by Mast that form in ameba is dependent on 

water content. 

Digestion. — Food is ingested 
directly through the ectoplasm^ 
and having entered the endoplasm, 
minute quantities of HCl secreted 
around the food mass form a gas- 
tric vacuole. Carbohydrates are 
not acted upon to any extent, 
digestion being chiefly limited to 
protein and fat. Solid wastes are 
extruded at any point, the ameba 
moving away and allowing the 
weighty excrement to pass 
through the ectoplasm. Ameba 
can nip a paramecium in two, engulfing one-half, and leaving the 
other half outside. 

Circulation. — There is no definite distribution of food materials 
but the movements of the animal thoroughly distribute the food 
granules. 

Respiration. — Oxygen is taken in through the whole surface of 
the body, and CO2 is extruded. The contractile vacuole is also im- 
portant in the interchange of gases. 

Excretion. — Besides the ejection of solid feces by merely leaving 
them behind as the animal moves forward, the contractile vacuole 
definitely functions in the excretion of liquid and gaseous wastes. 

Reproduction. — The ameba is able to divide its nuclear and cyto- 
plasmic constituents equally, the process being called binaj-y fission 
or division. Under adverse conditions or sometimes solely for 
reproductive purposes the ameba encysts. It then forms daughter 
cells which mature in about three weeks. The number produced 
varies in different species. 

Nervous System and Reactions. — Without nerve cells or fibers, 
the ameba is still a complete neuromuscular organism. It reacts 
to all sorts of stimuli, including light, heat, touch, gravity, currents 
of water, chemicals, and electricity. 

Tropisms. — The term "tropism" has long been used to indicate 
the reaction of an animal to some sort of stimulus. A few of the 



I 



PROTOZOA 



^5 



tropisms are indicated: (i) Photo tropism, or heliotropism — reaction 
to light. (2) Geotropism — reaction to gravity. (3) Rheotropism 
— reaction to currents (stream pressure). (4) Thermotropism — re- 
action to heat. (5) Thigmotropism — reaction to touch or contact. 
(6) Chemotropism — reaction to a chemical. (7) Galvanotropism 
— reaction to electrical currents. 

In general we find that for any animal there exists an optimum 
attracting stimulus, which we may term positive tropism (or taxis) ^ 
and a negative stimulus, usually the more powerful one. For 
example, the ameba will be positively phototropic to a certain light, 
but negatively phototropic to one of greater intensity. 

Orders of Sarcodina. Order i. — Lobosa — (Ameba) soft jelly-like 
— 5-200 ii. in diameter. They are found in pools of stagnant water. 
Each species assumes its characteristic shape (Fig. 3 A). They are 
full of granules and have one or more nuclei and a contractile vacu- 
ole. They reproduce by simple fission, by sporulation, and rarely 
by conjugation. 

Order 2. — Foraminifera. They have a test or shell full of 
openings, through which project filose pseudopodia. They are 
chiefly marine, varying in size from microscopic to two inches in 
diameter. Their shells are calcareous, siliceous and chitinous 
(horny). There are 120 species of Foraminifera in English chalk 
clifi^s. The Norfolk chalk measures are 1,450 feet thick. Globi- 
gerina ooze forms gray chalk which is deposited on the bottom of the 
ocean to depths of 2,500 fathoms. They reproduce by motile swarm 
spores and by binary fission. Sometimes young with shells are 
formed in the terminal chamber of the adult. The nummulites, the 
largest of the foraminifera, are as large as a silver dollar. The 
limestone pyramids of Egypt are full of nummulites. 

Order J. — Heliozoa are mostly found in fresh water. They have 
fine stiff radiating pseudopodia. Some have skeletons of delicate 
siliceous spicules. Some species are colonial. Reproduction is by 
fission^ spore-Jorrnation and by conjugation (Fig. 4). 

Order 4. — Radiolaria are all marine. They differ from Heliozoa 
in having a much more elaborate skeleton of siliceous or other 
mineral substance. They have a central capsule surrounding the 
nucleus. They are united to form colonies of various shapes in some 
groups. Fossil radiolaria are found in slate, flint, chalk and deep 
sea deposits. 



26 



PROTOZOA 



Reproduction. — {a) Binary fission. The nucleus divides first, 
then the central capsule, then the extra-capsular tissue, {b) Spore- 
formation. The intra-capsular protoplasm divides into small 



^' Egested particle 




Nucleus 



Con f roc tl/e vacuole 

Fig. 4. Actinosphaerium, a Heliozoan. (Drawn by H. N. Lammers. After Leidy.) 

masses, each of which becomes a flagellula with a single flagellum. 
Sometimes the spores produced are alike, in others they are di- 
morphic some being microspores and others megaspores. 

Symbiosis of Radiolaria. — Radio- 
laria and algae (yellow cells) live in 
symbiotic relation. (See page 482.) 
The radiolarian supplies CO2 and N 
waste. The alga gives off O and 
makes sugar. 

P arasitic S arcodina. — Lambl 
(i860) discovered an organism in 
feces of a child and decided that it 
was connected with diarrhea, but 
later rejected this opinion. Later 
(Afte7calkTns757o%;;'7/irPro- Lewis and Cunningham (1870) found 
tozoa. Courtesy of Lea and amebae in the feces of nearly 20 per 
Febiger.) cent of cholera patients examined in 

India. They were not the cause of 
cholera, however. Other investigators found two species of ameba 
in the intestine of man, one harmless, Entameba coli^ one causing 
dysentery^ Entameba histolytica (Fig. 5). 



E-ndosome —- 

Cor lex of 

chromalin 



Fig. 5. Endamoeba intestinalis. 




PROTOZOA 



27 



Entameba buccalis {gingivalis) , found in the mouth around carious 
teeth, is considered one of the causes of Pyorrhoea alveolarisJ^ 

Class 2. Mastigophora (Flagellates). Type of Group — Eu- 
glena. — Certain intermediate forms called Mastigamebae (Fig. 7) 



...Girdle 
-- Tooth 




!l7"ii Longitudinal 

Flagellum 



.Tentacle 



Fig. 6. Noctiluca scintillans, postero- ventral view. (Courtesy of C. A. Kofoid.) 

have not only the changeable shape and pseudopodia of the ameba, 
but are provided with a flagellum in addition. There is apparently a 
direct evolution from the pseudo- / 



podium to the flagellum. 

The true flagellates may have 
one or more flagella. Some- 
times one flagellum is used for 
locomotion and another as an 
anchor. Some forms have cellu- 
lose tests and some are without 
any shell or case. One group of 
marine flagellates have siliceous 
skeletons similar to those of the 
Radiolaria. Reproduction is by 
simple longitudinal division. 



' FlocjeUum 

„V(/> P^eudopodi-um 



Fig. 7. 



Mastigameba aspera. (Calkins. 
After F. E. Schultze.) 



Sometimes encystment occurs. 

Euglena is a green flagellate found in fresh water associated with 

3 Kofoid, C. A. 1929. The protozoa of the human mouth. Jour, of Paras., vol. 
15, pp. 1 51-174. 



28 



PROTOZOA 



Profoplosmic 

Jnclusion 

F/oge//um 

Bleph aroplas t 
Eyespo t 

Reservoir 



Other protozoa and with many of the algae. At times used in 
elementary courses by botanists, since it furnishes the movement 
so necessary to intrigue the student, it is unquestionably a plant- 
animal. Its shape is roughly that of a cigar and it moves through 
the water by means of a flagellum (Fig. 8). 

The body is covered by a cuticle, the external portion of the 

ectosarc. The endosarc contains 
the gullet, a reservoir, contractile 
vacuoles, chromoplasts and a 
nucleus. 

Some authors have claimed 
(apparently without observa- 
tion) that Euglena does not in- 
gest solid particles. The writer 
has observed with a class of 
thirty students a whole culture 
of Euglena in the act of ingest- 
ing food granules. The animal 
thrives best, however, when 
given abundant sunlight. It is 
quite evidently one of those 
Phytozoa which is able to utilize 
chlorophyll as well as to ingest 
solids. 

The red " eye-spot " is ap- 
parently composed of material 
with the power of absorbing 
light. Reaction to shadows 
occurs in Ruglena. just he/ore the 
pigment spot reaches the shaded 
region. In Volvox, a colonial 
flagellate, each cell has a true 
" eye-spot." Strong light produces negative phototropism. 

Economic Importance of Flagellates. — Uroglena not only colors 
drinking water yellow, but produces a fishy oily odor similar to that 
of cod liver oil. Peridinians (Gonyaulax) sometimes turn the sea 
red as blood off the coasts of California, Australia and India. They 
remove the free oxvgen from the water and cause suffocation of the 
fish. Synura tivella produces in drinking water a bitter spicy taste 
resembling that of ripe cucumbers. Dinobryon, also a colonial form, 




Nucleus 



— Fttramy/on body 



Pyrsnoid 



Fig. 8. Euglena gracilis. (Drawn by H. 
N. Lammers. After W. B. Baker.) 



PROTOZOA 



29 



has a fishy odor similar to seaweed. Cristispira is the large flagellate 
found in the crystalline style of clams and oysters. 

Trypanosoma gambiense^ found in Southern Africa, causes sleep- 
ing sickyiess in man. It is known to be transmitted by the bite of 
Glossina palpalis^ the tse-tse fly. Other species of tse-tse flies 
transmit different species of trypanosomes to mammals. Try- 
panosoma brucei causes the tse-tse fly disease of cattle in tropical 
Africa. The Germans claim that 
a drug called Bayer 205 is a 
specific for sleeping sickness. A 
remedy for paresis, tryparsamide, 
developed at the Rockefeller Insti- 
tute, has been substituted for the 
German patented preparation, and 
reported successful. 

Leishmania transmitted by in- 
sects cause Leishmaniasis or infan- 
tile ulcer, and tropical ulcer. Surra 
and dourine are trypanosome dis- 
eases of cattle and horses. 

Giardia ( Lamblia) inlestinalis, 
parasitic in the duodenum of man 
and the rodents, causes diarrhoea. 
The parasite is specific for each 
mammal. 

Histo)nonas meleagridis causes 
black-head (entero-hepatitis) o f 
turkeys. It is a small degenerate 
flagellate of the trichomonad type, 
which in tissues, loses its flagella. 

Symbiosis. — Symbiosis between 
termites and protozoa has been 
discussed by Cleveland {Science, 
vol. 61, no. 1585, p. 520) who has 
shown that the intestine of wood-feeding termites contain small 
flagellate protozoa, which may be removed by incubation, starvation, 
or oxygenation without killing the termites. Neither organism can 
live very long without the other, the termites dying three or four 
days after the protozoa are taken from them. Cleveland empha- 
sizes the fact that oxygenation will destroy ciliates and flagellates 
found in cockroaches as well. 




Fig. 9. Giardia maris. AX, 
axostyle; 5, blepharoplast; BB, basal 
body; C, centriole; E, endosome; N, 
nucleus; PL, parabasal body; RH, 
rhizoplast. (Calkins. After Kofoid 
and Swezy.) 



30 PROTOZOA 

Class 3. Infusoria. — In the Infusoria we find that the body is 
provided with cilia useful in locomotion and the ingestion of food. 
All Infusoria possess cilia in at least the immature condition, but in 
a few forms they are replaced in the adult by tentacles. 

Subclass 1. Ciliata. — Infusoria having cilia throughout life. 
They have a mouth, often with an undulating membrane. They 
include five orders. 

Order i. Holotricha. — Primitive Infusoria with small uniform 
cilia arranged in more or less spiral rows. (Examples: Paramecium^ 
Colpoda.) 

Order 2. Heterotricha. — Infusoria in which small cilia are found 
covering the body while the peristome is bordered with a spiral of 
large adoral cilia. Fusion of the cilia into membranelles produces a 
direct pathway to the mouth. (Example: Stentor.) 

Order j. Oligotrichida. — In this order the adoral zone forms a 
ring around the margin of the peristome. Cilia are greatly reduced 
or absent, and membranelles are the only motile organs. There are 
three families, two of which are free living ( Halteridae and Tintin- 
nidae), and the third consists of parasitic forms {Ophryoscolecidae) 
in the stomach of ruminant mammals. (See page 482.) 

Order 4. Hypotricha. — Ciliata with a dorso-ventrally flattened 
body. The dorsal surface has longitudinal rows of vestigial cilia 
in the form of spines, while the ventral surface has hooks, fans, and 
fringed plates. The hooked cirri act as legs. (Examples: Stylo- 
nychia, Oxytricha.) 

Order 5. Peritricha. — Ciliata for the most part bare of cilia, 
except in the oral region, and in some species with an aboral circlet 
of cilia. The peristome bears a spiral band of large cilia, which 
continues around the lid-like disc marking the distal end. Many of 
the Peritricha are attached by a stalk which contains a contractile 
fiber. (Examples: Vorticella, Epistylis.) 

Subclass 2. Suctoria {Jcinetaria, Teniae ulif era). — Infusoria 
which have cilia in the young condition, but tubelike tentacles in 
the adult. They have no locomotor organs except in the free- 
swimming young, and are attached by a stalk. Other Infusoria are 
caught by the tentacles and after the cuticle has been dissolved, the 
fluid protoplasm is sucked down into the body of the suctorian. 
(Examples: Podophyra; Dendrosoma, a colonial form.) 

Subclass 1. Ciliata. Infusoria. Order i. Holotricha. Type 
— Paramecium caudatum. — Paramecium is a slipper-shaped, ciliated 



PROTOZOA 



31 












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V 


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< 


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-t^ 


s^ 


:) 


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c: 


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32 PROTOZOA 

animal found active in infusions of decaying vegetation. It is 
readily obtained from hay immersed in water (Fig. lo, A and E). 

The outer covering or ectosarc has at its outer edge a thin 
cuticle which tends to keep the animal of the same shape although it 
is able to bend laterally. An oral groove running obliquely from the 
anterior end to about the middle of the body aids in producing a 
spiral movement as the cilia beat. The cilia are found all over the 
body in spiral lines, and are especially prominent along the oral 
groove and along the anterior and posterior ends. Under the cuticle 
the ectoplasm contains a layer of protective organs called tricho- 
cysts. The trichocysts in Epistylis umbellaria, a peritrichous 
ciliate, are found in minute capsules arranged in pairs, each con- 
taining a coiled thread. They are similar to the nematocysts, which 
are characteristic of Coelenterates. The endoplasm contains 
vacuoles, nuclei and food balls of ingested bacteria which traverse 
the endoplasm along a definite path. 

Locomotion. — The cilia beating violently in unison direct the 
animal forward, or reverse it, and the spiral lines give the spiral 
rotation which keeps the course of the animal in a straight line. 

Digestion. — The cilia lining the oral groove direct particles of 
food towards the mouth, and an undulating membrane (formed by 
fused cilia) forces them down the gullet and into the interior of the 
animal. The same type o{ gastric vacuole characterizing the Ameba 
is found in Paramecium, Microchemical determinations have 
shown that dilute HCl is formed around the food particles and that 
protein digestion takes place. Excretion of indigestible material 
is through a definite excretory aperture, the anus. 

Circulation. — As in Ameba we find no circulatory canals. The 
action of the two contractile vacuoles removes fluid. Water is 
taken in by the mouth with the food which is distributed in the 
movement called cyclosis. 

Respiration. — Oxygen is taken in, and CO2 is extruded, through 
the whole surface of the animal. The contractile vacuoles aid in 
gaseous interchange. 

Excretion. — Indigestible material not attacked by the HCl in the 
food vacuoles is extruded at once along the oral groove by the 
reversal of direction of the ciliary beat and the contractile vacuoles 
are supposed to aid in excretion of liquids and possibly of nitrogenous 
wastes, as well as gases. The anal aperture extrudes wastes subse- 
quent to digestion. 



PROTOZOA 



33 



Reproduction. — Paramecium reproduces by simple binary fission 
and frequently conjugates. Isolated daily, the offspring of a single 
Paramecium have been kept running since 1907 by Woodruff of 
Yale University. Over 13,500 generations have been produced by 




FiffST MATURATION DIVISION OF MICRONUCLEUS 



3EC0N0 AND TMIRn 
DIVISION OF MICRONUCLEUS 





THREE 5OMAT1C DIVISIONS OF FERTILIZED NUCLEUS 



rERTIUZATlON 



TWO CONSECUTIVE DIVISIONS 
GIVING FOUR NORMAL CELLS 




Fig. II. Conjugation in Paramecium caudatum. (After Calkins.) 

division without an opportunity for conjugation with a different 
line^ (Fig. 10, J and B). 

* Woodruff, L. L. 1929. Thirteen thousand generations of Paramecium. Proc. 
Soc. Exp. Biol, and Med., vol. 26, pp. 707-708, May. 



34 



PROTOZOA 




isi 



\-.in 0. 



Conjugation. — The nuclear elements of Paramecium are of two 
kinds. The nutritive or somatic nucleus (macronucleus), consider- 
ably larger than the reproductive or sexual nucleus (micronucleus), 
is responsible for the meta- 
bolic activities of the animal. 
If a Paramecium is cut in 
two, the part containing the 
two nuclei will survive, but 
the other half will die. The 
reproductive nucleus as- 
sumes importance in conju- 
gation and sexual reproduc- 
tion and the nutritive nucleus 
then temporarily disappears 
(Fig. 1 1 ) . Parameciu7n aurelia 
has two reproductive nuclei. 
Preliminary to conjuga- 
tion the oral surfaces of two 
animals are united by a pro- 
FiG. \iA. Lacry- toplasmic bridge. The re- 
maria sp. productive nucleus goes 

through the maturation pro- 
cess, divides twice formingfour gametes, three of 
these degenerate, the survivor divides, forming 
a resident/^;w«/^ pronucleus and a j-;;2^//migrant 
male pronucleus . Each male pronucleus passes 
across the protoplasmic bridge into the endo- 
plasm of the other animal and fuses with the 
female pronucleus, thus fertilizing it, forming 
the zygote nucleus. After mutual fertilization, 
the fusion nucleus of each animal divides by 
indirect division (see p. 500 for mitosis) into 
two and finally into eight nuclei equal in size. 
Four of these develop into nutritive or somatic 
nuclei, and four into reproductive or sexual ambiguum. (After Stem. 

nuclei. Transverse divisions (simple fissions) F''^";^ Calkins 5/./o^j oj 
. . . . , 1 • 1 . . the Protozoa. Courtesy 01 

result m four animals, each with a nutritive L^a and Febiger ) 

and a reproductive nucleus. 

Conjugation has been supposed to be necessary to prevent 

degeneration of Protozoa, but experiments previously mentioned 



i! 



Fig. \iB. Spirostomum 



PROTOZOA 



3S 



have proved that Paramecium is potentially immortal. 

Nervous Systejn and Reactions. — On account of its rapid loco- 
motion, Paramecium has been used a great deal in studies of be- 



^^^' ^.■'••••••'-,.'ii,'^-t^ 



-.>..«> : b: . 







^''^> ; 






Fig. 13^. Chilodon. (After M. ^4- MacDougall.) 5. Colpoda cucullulus. 
(After Biitschli.) C. Podophyra sp., a Suctorian. (After Calkins, Biology of the 
Protozoa. Courtesy of Lea and Febiger.) 



havior. Jennings has shown that Paramecium responds positively 
to contact, gravity and to running water, and that its behavior with 
reference to stimuli of light, chemicals, electricity and heat depends 



36 



PROTOZOA 



upon the force of the stimulus, In some cases the reaction being 
positive and in others negative. 

Economic Importance of Ciliates.^ — Bursaria is said to produce 
an odor in water supplies similar to that of a salt marsh. Vorticella 
and Stentor (Fig. 14, A) are frequently found in "'pipe moss " and 
along edges of reservoirs and dams, but are not injurious. Ciliates 
clean up bacteria in sewage disposal plants. 



Fig 



^r Nucleus 




ff~^ ^^//e/ 



Controcfile i/ocuo/e 




Stentor sp. (After Stein. Drawn 
by H. N. Lammers.) 



Fig. i^B. Opalina. (After 
Biitschli. Drawn by H. N. 
Lammers.) 



Parasitic Ciliates. — Balantidium coli and Balantidium minutum 
have been found in the intestines of human beings infected with 

® In considering the value of Protozoa, we must remember that they are mar- 
velously adapted to laboratory experimentation. Calkins, Woodruff, Jennings, and 
others have demonstrated this by a variety of fundamental studies on life processes. 
Packard has studied the influence of salts on the division rate of Paramecium, adding to 
our information facts which may have significance in efforts at the control of cancer. 
(Packard, C. 1926. Effect of sodium on the rate of cell division. Jour, of Cancer 
Research, vol. 10, pages 1-14.) 



PROTOZOA 37 

dysentery and are thought to be concerned with certain ulcers of the 
large intestines. 

Opalina (see Figure i^B) is parasitic in the intestine of the frog 
(Metcalf). Several species of ectoparasitic infusoria are known to 
attack fishes, causing inflammation and death. Ichthyophthirius 
attacks steel-head-trout fingerlings, catfish, bass and perch. The 
common stickleback is one of the carriers for the parasite. 

Cyclochaeta and Chilodon are parasites of goldfish, brook trout 
and small mouth black bass but apparently do not infest salmon, 
steel-head trout or perch. Cyclochaeta thrives best when the 
temperature of the water is low, below 50° F., but Chilodori cy print 
requires a higher temperature (Guberlet). 

, • ■ ' f .• 







oneme around moafh 
Phoryngeol boskef 



\r^:^^:^-^m-^- "^ol/road track' 



Fig. 15. Neuromotor apparatus of Chlamydodon. (After M. S. MacDougall. Biol. 

Bull., vol. 54, p. 473, 1928.) 

Class 4. Sporozoa. Type — Plasmodium vivax. — The Sporozoa 
lack organs of locomotion and are characterized by their method of 
reproduction by spore formation. They are all parasitic forms at 
the active stages of their life cycle. 

The malarial Plasmodia include three species. One, P. vivax., 
produces chill every 48 hours; another, P. malariae, causes chill 
every 72 hours; while the third, P. falciparum., produces attacks 
daily or at irregular intervals (Fig. 16). 

Infected/d-zw^/^ mosquitoes of the Anopheline group are able to 



38 



PROTOZOA 



transmit the organisms. The blood of a malarial patient containing 
gametocytes is sucked up into the alimentary canal of the mosquito 
where the gametocytes produce matured macrogametocytes (egg) 



Some may be taken 
into the stomach 
of the niosquitowhen 
it bites 



luman 






Development of 
Parasite in 

6: 



InSalivary Development 
Gland 
(SffTlosq. 

in the 

rPosc^uito 

'/ /In Body 

' L Cavity of moscj. 




'^^oscj. Storo2^^^ 




Fig. i6. Life history of tiie malarial organism. (After Kellogg and Doane. Courtesy 

of Henry Holt & Co.) 

and flagellated microgametocytes (sperm) which conjugate and form 
a zygote or ookinete which grows into a multicellular somatella or 
sporoblast in a cyst in the wall of the stomach. This cyst liberates 



PROTOZOA 



39 




...e 



-« 



thousands of tiny sporozoites which collect in the mosquito's 
salivary glands. If the mosquito afterwards bites a human being 
some of the sporozoites from the wound may be introduced and will 
enter the red blood corpuscles, and when sufficiently numerous will 
produce a chill. Such chills occur at the end of every 48 hours with 
each recurring cycle of sporulation, in the case of Plasmodium vivax. 
Quinine, the specific against malaria, may be resisted by certain 
of the malarial parasites in the spleen or bone marrow. 

Orders of Sporozoa. Order i. Gregarinida. — 
Monocystis is an abundant parasite of the seminal 
vesicles of the earthworm. Porospora gigantea (two- 
thirds of an inch long) is parasitic in the alimentary 
tube of the lobster. 

Order 2. Coccidia. — Coccidia cause red dysentery 
in calves and infest the liver and intestine of man 
and other vertebrates, besides oysters, insects and 
Crustacea. At least five species of Eimeria occur in 
chickens. One of these is very destructive to young 
chickens. 

Order ?. — Haemosporidia live in the blood. The 

r -I- 1 T-»I J- J J U tic. 17. A 

two important families are the Flasmodidae and the poiycystid 

Babesidae. gregarine. 

The Plasmodidae include the malaria organisms. Wasielewsky. 

They induce malaria in birds and mammals. Plus- (From Calk- 

modium vivax causes tertian fever, P. malariae causes ":^' '° °^/ 

• 1 r of the rroto- 

quartan fever and P. falciparum causes tropical tever. .^^ Courtesy 

Paresis has recently been treated successfully by of Lea and 

infecting the patients with malaria. The organisms Febiger.) 

are transmitted by Anopheline mosquitoes. (See Fig. 

89.) O'Roke (1930) has found a fatal malarial disease in quails 

transmitted by a degenerate fly, Lynchia, living in the feathers. 

The Babesidae include several important blood parasites, all of 

which are transmitted by ticks. Babesia bigemina, the organism 

producing Texas cattle fever, is transmitted by the bite of the tick 

Boophilus annulatus. Death occurs in acute cases in two days. 

Trypan-blue has been used in the treatment of babesiasis. Babesia 

canis, the organism attacking dogs, has been the most studied. 

East Coast fever is caused by Babesia parva which is found in the red 

blood corpuscles of cattle, producing anemia. Oroya fever is a 

human disease occurring in mountain valleys of Peru. It is a 



40 PROTOZOA 

severe anemia associated with irregular fever, caused by Bartonella 
bacillijormis. 

Order 4. — Myxosporidia cause epidemics in fishes and silk worms. 

Order 5. Sarcosporidia. — Sarcocystis is found in the muscles of 
pig, mouse and man. It has been suggested that the larvae of flies 
may transmit Sarcosporidia. 

General Considerations 

Protozoa are generalized single cells. They are differentiated into 
ectoplasm and endoplasm. All organs of locomotion and defense 
are from the ectoplasm. The seat of digestion and other functions 
is the endoplasm. All Protozoa have a nucleus. There is generally 
one but very often Protozoa are multinuclear. Other forms, 
Infusorians, have two nuclei, one macronucleus and one micronu- 
cleus. The former may be chain or dumb-bell shaped. 

Locomotion. — The organs of locomotion in Protozoa are pseu- 
dopodia, flagella or cilia. The ciliates are extremely speedy in 
movement, while many of the flagellates scull rapidly. Shipley 
found that in the case of four amebae given ten trials, the fastest 
moved 0.2 of a mm. in 60 seconds, while the slowest moved that 
distance in 80 seconds. 

Nutrition. — Nutrition consists of capture and ingestion, digestion 
and defecation. It may occur also by osmosis. 

(i) Many organisms can build up complex proteins from simpler 
chemical materials. There are holophytic plant-like types in which 
sunlight energy is used in synthesis and saprozoic forms in which the 
protoplasm is built up from organic substances in solution. 

(2) Other organisms are entirely dependent on a supply of 
protein ready made, obtained either by the holozoic method — by 
engulfing and digesting other living organisms; or as parasites — by 
feeding on digested foods. Parasites generally absorb their food in 
an osmotic manner rather than by engulfing it. Some species of 
Euglena are holophytic and others saprozoic. Some species in the 
life of one individual are holophytic in the sunlight and saprozoic in 
the dark. 

Ingestion. — The ameba type is enclosing; but vortex currents are 
set up by the cilia in Ciliates while the Suctoria pour their endoplasm 
into an animal, digest it and then suck it through their tentacles. 
Wenyon states that enzymes probably aid in liquefying the protein. 



PROTOZOA 41 

Digestion is always intracellular and in the endoplasm. Gastric 
vacuoles contain fluids taken in with the food. Water is modified 
by osjnosis to become a digestive fluid weak in HCl. At the begin- 
ning of the digestive process, when food matters are first ingested, 
there is a remarkable secretion of acid. This secretion ceases with 
the beginning of the breakdown of food materials. Usually there 
is a distinct alkaline reaction in the food vacuoles. Proteins are the 
main sources of nutrition; starch is affected but slightly, but it is 
claimed that the Rhizopoda dissolve starch grains and even cellulose. 

Few protozoa are known to digest fats, but oil droplets and fat 
bodies are found in practically all of the protozoan groups. Dawson 
and Belkin have shown "^ that Ameba dubia and A. proteus are able 
to digest several of the oils, including peanut oil and olive oil. 

Some of the injurious bacteria may serve as excellent food for an 
ameba. Rndameba coli ingests intestinal bacteria and Endameba 
histolytica engulfs red blood corpuscles. Kofoid finds that a flagel- 
late {Pentatrichoinonas) ingests red blood corpuscles. The majority 
of protozoan parasites absorb food by osmosis. Some Ophryo- 
scolecidae eat chlorophyll grains. 

Excretion is by osmosis and also in the majority of Protozoa by 
one or more contractile vacuoles. Contractile vacuoles are formed 
in the endoplasm by accumulation of liquid. The cause of their 
contraction is unknown. Probably the contractile vacuole is also 
a respiratory organ. In one-half hour a protozoan throws out a 
quantity of water equal to the size of its body. 

Irritability. — The Protozoa are sensitive to nearly all stimuli. 
There is not satisfactory evidence of color vision, although many 
forms react to changes in light intensity. With regard to reaction 
to the pull of gravity it is argued that this is not a true positive 
geotropism (p. 25) in Paramecium. The Protozoa react to tem- 
perature changes, chemical and electrical stimuli. Ameba is a 
complete neuromuscular organism capable of responding to stimuli 
without correlation. Reproduction in Ameba coiiijiAlA of. ( i ) sim p le 
TJi^ J oi c m o r fiooion^ a). -buddrng^-Xg^-^p ere formatioti ^ 

Reproduction and Regeneration. Reproduction in the Sarco- 
dina. — (i) Fusion of two amebae is said to occur, resulting in a new 
organism. The significance and results of such a procedure are 
unknown. Such a process has been compared to the fusion of the 

7 Proc. Soc. Exp. Biol, and Med., 1928, vol. 25, pp. 790-793; and Biol. Bull., 1929, 
vol. 56, p. 80. 



42 PROTOZOA 

sperm with the egg but no cytological proof of zygote formation has 
been achieved. (2) Sporulation or encystment occurs in Ameba. 
The animal becomes spherical, secretes three-layered cysts and 
produces, by successive divisions of the nucleus, a multicellular 
somatella containing 2, 4, 8 or more nuclei. The Ameba divides 
at encystment into as many individuals as there are nuclei in the 
somatella. These emerge through a pore from the cyst as amebulae 
and in a few hours develop into full grown amebae. (3) Fission. 
In some forms, division (binary fission) takes place during activity; 
in others it takes place in a cyst. (4) Budding. In Euglypha, the 
animal buds and new particles go out from the shell. Simple division 
in Protozoa may lead to colony formation. (5) Conjugation in the 
Sarcodina is general, except in Lobosa and an investigator thought 
that he had seen it in Ameba proteus. This may have been only 
agglutination. (6) There is no evidence of reorganization, or 
endomixis (see page 44) in the Sarcodina. 

Regeneration in the Sarcodina. — The excision of one-fourth of 
the cytoplasm of the Ameba has no effect on its division. Regenera- 
tion may take place in twenty-four hours and division follows nor- 
mally. Enucleated amebae can move, but are not able to carry on 
other body processes and soon die. 

Reproduction in the Flagellata. (i) Fission. — With but few 
exceptions the flagellates have longitudinal fission. (2) Encystment 
and sporulation also occur at times. 

Reproduction in the Ciliata.^ (i) Fission. — All ciliates have 
transverse division. The reproduction of the macronucleus is 
usually by direct division with little evidence of spindle formation 
or definite chromosomes. In less complicated types of division, 
the division of the macronucleus is relatively simple. In some forms 
the macronucleus elongates, then constricts to form two equal 
portions, one passing to each of the daughter cells {Paramecium, 
Colpoda). When two macronuclei are present, each divides inde- 
pendently of the other {Oxytricha, Stylonychia). In some types 
multiple macronuclei may contain nuclear clefts with large granules 
which reproduce by division. Micronuclei, if multiple in the cell, 
do not fuse. The chromatin contents may be in part distributed and 
then unite into a long banded nucleus. No elimination of micro- 
nuclear material occurs. Each one divides by mitosis, with a 

* Consult Robertson, M. 1929. Life cycles in the Protozoa. Biol. Rev., vol. 4, 
no. 2, April. 



PROTOZOA 



43 



definite number of chromosomes, (2) Conjugation is typical of the 
Ciliata (see p. 23)- (3) Encystment and sporulation are characteris- 
tic of many forms like Colpoda. In spore-formation there are many 
simultaneous divisions. 

Encystment, while characteristic of the Sporozoa, is found in ail 
classes of the Protozoa. Motor organs are withdrawn and the ani- 
mal forms a test or shell excluding the water, and becoming en- 
cysted or fixed. 

"In the majority of cases (Minchin, p. 165) an individual in the process 
of encystment becomes perfectly spherical; occasionally ovoid or pear 
shaped. Any food particles or foreign bodies are usually ejected or ab- 
sorbed, contractile vacuoles disappear, all locomotor organs absorbed or 
cast off. The protoplasm of the organism becomes less fluid and more 
opaque. Lastly the cyst membrane itself appears around the body. It 
stands off distinctly from the rest of the body and may vary from a soft 
slimy or gelatinous coat to a firm membrane, often tough and impervious." 

Protozoa in the encysted state are able to withstand drying, 
freezing or sun baking. They may be transmitted by winds or 
birds to a great distance. In parasitic forms, encystment is an 
adaptation connected with a change from one host to another. 

In the spo?'OZoan parasites y two forms of cysts are distinguishable: 
I. Full grown forms may produce large resistant cysts, spherical 
or oval in form. 2. Smallest forms in developmental cycle, the 
products of multiple fission or sporulation, may secrete around them- 
selves tough resistant envelopes, within which they may multiply 
further. In this case, the envelope is the sporocyst and the entire 
body a spore. " The spores of bacteria are for the most part simply 
cysts, but are called spores on account of their small size " (Minchin, 
p. 166). 

The functions of encystment are: i. To protect during adverse 
conditions. 2. For purpose of digestion after a heavy meal. 3. 
Reproduction. 4. Reinfection. 

It should perhaps be emphasized at this point that some ciliates 
(Colpoda) divide on/y after forming a division cyst. 

Regeneration in the Ciliata is a phase of growth. Ciliata with 
the macronucleus (nutritive nucleus) will live since this nucleus 
supervises constructive metabolism. Yet Dawson showed that 
Oxytricha, lacking a micronucleus, would live for 289 generations, 
from July 10, 1917, to Nov. 17, 1919, without conjugation, reor- 
ganization (endomixis), or encystment. 



44 PROTOZOA 

If Stentor is cut into two pieces, any part containing a portion 
of the nucleus will regenerate readily. 

Endomixis. — There is some controversy over the significance of 
the complete nuclear reorganization without cell fusion first de- 
scribed by Woodruff as occurring periodically in pedigreed races of 
Paramecium. At regular intervals of about 30 days, in Parameciurn 
aurelia (sixty in P. caudatum) the old jnacronucleus gives rise to 
buds or fragments which are absorbed in the cytoplasm. Each of 
the micronuclei divides twice, which forms new products of both 
micro- and macronuclei. 

It is the belief of Calkins, from his investigations on Uroleptus, 
that " endomixis " is a satisfactory substitute for the fusion of 
different nuclei at conjugation. He holds that continued vitality 
is possible when either process furnishes the necessary reorganization 
of nuclear elements. Endomixis does not seem to be essential to 
all ciliates. It has been interpreted as parthenogenesis. 

Distribution of the Protozoa. — Even the most barren soils con- 
tain Protozoa, the same species being found in tropical, temperate, 
and arctic soils. The maximum numbers of soil Protozoa are found 
at a depth of 4 to 5 inches, but some species seem able to live under 
anaerobic conditions. Certain Protozoa thrive as internal parasites, 
and live in the blood or internal organs of other animals. 

The majority of the Protozoa, however, are aquatic. They are 
found from the deepest seas (5,000 fathoms) to a point 10,000 feet 
above sea level, Juday reported a fresh water anaerobic ciliate 
found in the centrifuged plankton of Lake Mendota. It appeared 
in water containing a minimum amount of oxygen. The maximum 
number (95,250) appeared in a litre of water from a stratum having 
no oxygen. 

Pack reported 1 ciliata, 9 algae, 5 bacteria, i crustacean and 2 
fly larvae in the water of Great Salt Lake which has 23 per cent 
salinity. Dilution of the medium caused a shortening of the cirri 
of the ciliates with increased size and activity. 

Fossil Relatives and Relationship to Other Phyla. — The Fora- 
minifera are of great geological importance, and are common as 
fossils from the Silurian rocks down to the present time. Today 
they are found in calcareous ooze, and are building beds of chalk 
and nummulithic limestone. 

The siliceous skeletons of the Radiolaria are found in slate and 
deep sea ooze. They aid in the formation of flint. (See p. 52.) 



PROTOZOA 

Economic Importance of Protozoa* 

Negative 



45 



Classes 


Positive 


Disease 


Organism 


Sarcodina 


Limestone 

Chalk 

Flint 


Amebic dysentery 


End. histolytica 


Flagellata 




Bad taste in drinking water 


Synura, Uvella, Dinobryon 






Sleeping sickness 


Tryp. gambiense 






Dysentery 


Giardia (Lamblia) 
intestinalis 






Tropical ulcer 


Leishmania 






Pyorrhoea 


Endameba buccalis 


Ciliata 


Experimenta- 
tion 


Odor in drinking water 


Bursaria (salt marsh smell) 






Dysentery 


Balantidium 
Opalina 


Sporozoa 




Malaria 


Plasmodium vivax 






Coccidiosis 


Eimeria 






Red dysentery 


Eimeria 






Silk worm disease 


Nosema bombycis 






Encysted in muscle, 


Sarcocystis 






degenerate it 





From the Tertiary deposits of the Barbadoes, Ehrenberg described 
278 species of Foraminifera, known today. 

We consider the Protozoa as the most primitive forms of animal 
life. Certain forms are so closely allied to the plants that they can 
scarcely be claimed exclusively by zoologists. 

The Sarcodina form an ascending series from the Lobosa, with 
no skeleton, up to the Radiolaria, which have well-developed 
skeletons. The Mastigameba is a Flagellate with pseudopodia, and 
we might consider it a connecting type between the two classes of 
Protozoa. The fact that Porifera have collar cells, somewhat 
resembling the flagellated protozoa, has led some zoologists to sug- 
gest the evolution of Choanoflagellata into Sponges. Kofoid finds 
in the colonial Dinoflagellata^ with nettling organs and eye spots, 
relationships to the Coelenterata. 

1 Negri bodies were at one time classed as Sporozoa, and later as Sarcodina, but 
they are now grouped with various other inclusions of diseased cells, such as in tra- 
choma, and sprue, as Chlamydozoa, or "mantle-covered" animals. Cowdry has even 
questioned whether the granules are microorganisms. Hurst suggests (Lancet, Sept. 
19, I931, p. 622) t\i3it rabies may have been transmitted in certain Trinidad cases from 
humans to cattle, by vampire bats. See also Knutti, R. E., 1929, Jour. Amer. Med. 
Assoc, vol. 93, p. 754. 



46 PROTOZOA 

References on Protozoa 

BuTSCHLi, O. 1889. Protozoa, in Bronn's Tierreich. 

Calkins, G. N. 1901. The Protozoa. Lemcke and Buechner, New 

York. 
Calkins, G. N. 1909. Protozoology. Lea and Febiger. 
Calkins, G. N. 1926. The Biology of the Protozoa. Lea and Febiger. 
Clarke, J. J. Protozoa and Disease. Pt. i, London, 1903; Pt. 2, 

London, 1908. 
Conn, H. W. 1905. Protozoa of Fresh Water of Connecticut. Bulletin 

Geological and Natural History Survey of Connecticut. 
Craig, C. F. 1926. A Manual of the Parasitic Protozoa of Man. J. B. 

Lippincott Co., Philadelphia, Pa. 
DoFLEiN. 1927. Lehrbuch der Protozoenkunde. Jena. 
Leidy, J. 1879. Fresh-water Rhizopods of North America. Govern- 
ment Printing Office. 
Minchin, E. a. 191 2. Introduction to the Study of the Protozoa with 

Special Reference to the Parasitic Forms. E. Arnold, London. 
Sandon, H. 1927. The Composition and Distribution of the Protozoan 

Fauna of the Soil. Oliver & Boyd, Edinburgh. 
Stitt, E. R. 191 8. Practical Bacteriology, Blood Work and Animal 

Parasitology, 5th edition. Philadelphia and London. 
Waksman, S. a. 1927. Principles of Soil Microbiology. Bailliere, 

Tindall and Cox. 
Ward, H. B., and Whipple, G. C. 191 8. Fresh-water Biology. John 

Wiley and Sons. 
Wenyon, C. M. 1926. Protozoology, 2 vols. Wm. Wood & Co., N. Y. 

Metazoa. (Gr. meta^ beyond; zoon^ animal.) — As we have al- 
ready shown (page 13), the Metazoa include all the Phyla above the 
Protozoa. The Metazoa begin as single cells, the fertilized eggs or 
ova, but early in their embryonic life they form two or three cell 
layers^ from which develop the organs and structures of the adult 
animal. The germ cells are functional in reproduction, while the 
body (somatic) cells carry on all other functions. To what extent 
the germ cells (germplasm) may be affected by the somatic cells 
(somatoplasm) and by environmental influences, is the basis of 
considerable controversy. (See page 514, Inheritance of Acquired 
Characters.) The somatic cells form tissues^ the discussion of 
which is deferred to a later chapter. (Page 426.) 



CHAPTER III 

PORIFERA 

PoRiFERA (Lat. porus, a pore; ferre^ to bear) were originally 
classed as colonial Protozoa. Found attached to rocks and other 
submerged objects, they resemble sea weed and were at one time 
considered as plants. With the exception of one family they are 
found in salt water. 

While sponges may reproduce by eggs and sperm, they com- 
monly reproduce by budding, colonies sometimes reaching a diam- 
eter of three feet. It is possible to cultivate them artificially since a 
complete sponge will develop from a single isolated cell. 

There are three kinds of sponges, the horny sponge used in com- 
merce, the siliceous sponges and the calcareous sponges, the last 
named having no commercial value. 

Classification 

Class I. Calcarea (Lat. calcarius, lime) with spicules of carbonate of 

lime. 
Class II. Hexactinellida (Gr. hex, six; aktiriy a ray) with siliceous 

spicules, in six rays. 
Class III. Demospongiae (Gr. demos, people; sponges, sponge) 

having spicules of silicon, or spongin. 

Characteristics 

1. Sponges are the simplest Metazoa, with two distinct layers, 

ectoderm and endoderm, and an undifferentiated middle layer, 
the mesoglea — which is filled with spicules of siliceous, horny 
or calcareous material. They are a community of cells with 
relatively little division of labor. 

2, There is no true coelom or body cavity, but the internal gastral 

cavity or cloaca ranges from a single tube to many branched 
chambers. 

a. Ascon — incurrent apertures pass directly into inner space. 

b. Sycon — cell layers folded — ectoderm and endoderm, central 
space. 

47 



48 



PORIFERA 



c. Leucon — external opening to canals, through orifices leading 
through ectoderm to endoderm. The water comes in the 

incurrent canal, then 
into the radial, then 
to the paragastric 
cavity. The radial 
canals are lined with 
Jiagella; all whip 
down and suck the 
water in. 
3. The general symmetry 
o f t h e embryonic 
gastrula stage is re- 
tained in the adult. 



Distribution. — The ma- 
jority of the sponges are 
marine, but there are a few 
fresh water forms (Spon- 
gillidae). They are found 
attached to rocks, sea weed 
and submerged objects. 
The true horny sponges are 
found in shallow water, not 
deeper than 450 fathoms. 
Other forms are found at 
great depths. 

Pigment in Sponges. — 
Many sponges contain pig- 
jnent. The lipochrome 
pigment zobyierythrin (seen 
in lobsters) is common. 
The green pigment of the 
fresh water sponge, analo- 
gous to chlorophyll, prob- 
ably aids in holophytic 
nutrition. 

Sponges vary in color 
from red brown to bright 
colors with pronounced 




Fig. 18. Top, commercial sponge. Center, 
the finger sponge. Bottom, red sponge. (From 
A. G. Mayer, SeasJiore Life. Courtesy of N. Y. 
Zool. Soc.) 



PORIFERA 49 

iridescence. The majority are gray in color. They vary in size 
from microscopic to several feet in diameter. Their shape, while 
frequently cylindrical, is quite variable. They may branch to 
form a network, or assume the shape of a fan, or even that of a hat- 
crown. (Figure i8.) 

Type of Group — Grantia. — Grantia is a cylindrical, vase-shaped 
marine sponge, somewhat less than an inch in length. It is readily 
obtained from submerged piles and rocks alongshore, and since it is 
convenient in size for external gross study, and can readily be 
sectioned, it is ordinarily studied in college courses. 

External Anatomy. — Grantia has an outer or dermal layer, 
consisting of epithelial cells, contractile cells, gland cells and poro- 
cytes. Lime spicules and spongin fibers are formed by the sclero- 
blasts, which belong to the inner portion of the dermal layer. The 
body wall consists of a skeleton of calcareous spicules of which there 
are four varieties, a long and a short scimitar shape, a trident shape, 
and a T shape. At times other four- and five-rayed spicules are 
noted. 

The middle layer is a jelly-like mesoglea, with wandering ameboid 
cells, which ingest, store and transport food materials. From time 
to time, germinal cells are here developed from some of the wander- 
ing cells, and form ova or spermatozoa. Gemmules (statoblasts) 
are formed in certain species. (See p. 50.) 

The inner or gastral layer lining the radial canals is made up of 
" collared " flagellate cells, or choanocytes, which create currents of 
water and bring inward particles of food. 

Ingestion and Digestion. (Figure 19.) — Food is ingested by 
specialized cells and digested as in protozoa. Some cells are for 
ingestion; the flagellated collar cells are extremely important in 
absorbing and taking up food. They form rather dense masses 
near the nuclei. Certain cells in the mesoglea are for storage, and 
still others are for nutrition. The sponges make use of detritus 
coming from dead plant and animal tissues found in sea water 
along the coast. Food vacuoles are formed as in the Protozoa. 

Circulation. — Circulation is by means of the ameboid wandering 
cells of the middle layer. Respiration is carried on by the cells of 
the body wall. Excretion is osmotic by cells, and also by the ex- 
pulsion of solids through the osculum. 

Reproduction, (i) Asexual. — Buds may arise near the base of 
the sponge and become detached as a separate individual, or in 



50 



PORIFERA 



some sponges colonies may be formed. Budding or branching is a 
common method of reproduction in sponges. 

In the fresh water Spongilla and in some of the marine sponges, 
the autumnal death of the adult sponge is preceded by the formation 
of statoblasts, or gemmules. The mesogleal cells aggregate in a 
clump, are surrounded by a firm membrane, and protected by blunt 
spicules, called amphidiscs. These gemmules survive the winter, 

and develop into males or 
females. From the ferti- 
lized eggs come the summer 
generation of sponges 
which produce gemmules 
and die in the fall. The 
gemmules serve to preserve 
the race, and to disperse it 
as well. They may be 
desiccated for years and 
then grow new Spongillae 
when the water returns. 

(2) Sexual. — Ameboid 
wandering cells from the 
mesoglea form eggs or 
spermatozoa. The ferti- 
lized eggs become flagel- 
lated free swimming larvae, 
then become fixed, pass 
through a primitive gas- 
trula stage, and finally de- 
velop the inhalant ostia 
and the exhalant osculum 
of an adult. The flagel- 
lated cells of the larva de- 
velop into the gastral choanocytes of the adult, and the larval inner 
cells develop into the dermal layer. 

Nervous System. — The first clearly marked neuromuscular cells 
in the Invertebrates are found in the sponges where certain " poro- 
cytes " are found surrounding the pores leading to the incurrent 
canals. There is no nervous receptor present, but the porocytes 
contract as do the Protozoa when stimulated. This may be called 
the independent-effector stage. Although the nervous system is thus 




Fig. 19. Longitudinal section of a simple 
sponge. 0, osculum; ip, incurrent pores. 
(Parker and Haswell, Textbook of Zoology. 
Courtesy of Macmillan and Co., Ltd.) 



PORIFERA 



51 



but little developed, the sponge reacts to stimuli. G. H. Parker has 
shown that the oscula (of Stylotelld) were closed in quiet sea water 
and on exposure to the air and to ether. The ostia (pores) opened 
in sea water currents and in fresh water and atropine, and closed in 
weak ether and cocaine. 

Habits. — Sponges furnish shelter for small organisms. They are 
inactive (sessile) and only open and close their openings. They are 
not eaten by fishes or even Arthropoda. Their strong odor and 







r' 



Fig. 



:o. Clam shell infested with boring sponge. (From A. G. Mayer, Seashore Life. 
Courtesy of New York Zool. Soc.) 



taste are important aids to the spicules in keeping enemies away. 
Micro-organisms that find their way through the pores are taken in 
as food by the phagocytic cells of the cloaca and radial canals. 
Sponges are not true parasites, but the boring sponge, C/iona, 
perforates the shell of oysters and other similar forms, seeking ^ro/^f- 
tion instead of food. (Figure 20.) 

Enemies of the sponges are bacteria, plant parasites and a few 
fish, which attack them when they are young. 

Associations. — Certain species of crabs (Dromia) are masked by 
sponges living as commensals, which profit by securing more oxygen. 



52 PORIFERA 

A compact orange-colored sponge {Suberites domunculd), of 
peculiar odor, grows around the shell inhabited by a hermit crab 
and dissolves the shell substance. Algae live in sy?nbiosis with some 
sponges. A cuttlefish {Rossia glaucopis) (see MoUusca, p. 154) puts 
its eggs in pockets in the substance of a siliceous sponge. 

Economic Importance. Positive. — i . The uses of the sponge are 
too well known to more than mention that they are of great im- 
portance in hospitals, homes, factories and garages. 

2. As an industry, sponge fisheries are of great value, probably 
being worth nearly two million dollars annually. In 1926 they 
brought in (Florida fisheries alone) $666,093.00. 

3. The siliceous sponges form flint deposits. 

Negative. — i. Sponges may kill oysters by boring into them. 
(Boring sponges.) 

2. They may attach to the oysters and starve them by taking the 
food first. 

3. They may actually reduce the oxygen of the water in their 
immediate vicinity by using currents first. 

4. Sometimes /r^j-A water sponges are of serious injury in that 
they attach to the walls of reservoirs and water pipes, and oflFer 
lodgment for fresh water mussels and Bryozoa. Various algae 
accumulate and the debris lodging against the miscellaneous or- 
ganisms produces a felt-like mass called " pipe-moss." 

5. The United States Department of Agriculture has published 
a bulletin on the reclamation of soil in Florida marshes showing that 
the sponge spicules wear away the hoofs of the mules used in plow- 
ing, while the shoes of the plowmen are worn through and their feet 
rendered raw in one day. 

Fossil Relatives. — Fossil sponges similar to existing groups have 
been found in formations from the Cambrian period down. They 
are chiefly found in chalk and flint. 

It has been estimated that a mass of sponge skeletons may give 
rise to beds of flint nodules in the space of fifty years. Siliceous 
sponges derive their spicules from small quantities of silicate in the 
sea water, originating from the decomposition of igneous rocks such 
as granite. The sponges and the Radiolaria (see page 44) furnish 
siliceous skeletons to aid in flint formation. The siliceous chalks 
are the first stage in the formation of flint. There is evidence from 
the casts of spicules found that the silica of sponge skeletons 
actually dissolved and was then redeposited. 



PORIFERA 



S3 



Ancestry and Relationship to Other Phyla. — Porifera are nearer 
the Protozoa than are any of the other types of Metazoa. The 
collar cells resemble certain colonial choano-flagellates . 

While the sponges somewhat resemble the Coelenterata, in 
having a fixed mode of life, in budding, and in having a large gastro- 
vascular cavity, the mode of formation of embryonic layers in the 
two groups shows radical dissimilarity. They are probably derived 
separately from the Protozoa. 

References on Sponges 

Cobb, J. N. 1902. The Sponge Fishery of Florida in 1900. Report of 

U. S. Fish Com. 
Davis, R. O. E. 1912. Sponge Spicules in Swamp Soils. Circ. No. 67, 

Bureau of Soils, U. S. D. A. 
Flegel, Ch. 1908. The Abuse of the Scaphander in the Sponge 

Fisheries. Bull. U. S. Bureau Fish., Vol. 28. 
Moore, H. F. 1908. The Commercial Sponges and the Sponge Fish- 
eries. Bull. U. S. Bureau of Fisheries, Vol. 28, part i, pp. 403, 

407-1 1, 426. 
Tressler, D. K. 1923. Marine Products of Commerce. Chem. Cat. 

Co., N. Y. 
Wilson, H. V. 1910. Development of Sponges from Tissue Cells 

Outside the Body of the Parent. Bull, of the Bur. of Fish., Vol. 28, 

pp. 1265-1271. 
Wilson, H. V. 1911, Development ot Sponges from Dissociated Tissue 

Cells. Bull, of the Bur. of Fish., Vol. 30. 
Consult, also, papers by Galtsoff, P., U. S. Bur. Fish. 




CHAPTER IV 



COELENTERATA 



The Coelenterata (Gr. koilosy hollow; enteron^ Intestine) are 
aquatic, and are for the most part marine, some developing into 
enormous colonies. Their bodies, especially the tentacles, bear 
nematocysts or " thread cells," structures not found in other Phyla, 
which are used for offense and defense. The corals, which secrete 
hard exoskeletons, are the most significant economically. 

Classification 

Class L Hydrozoa {Gr. hudra, wa.t€:r serpent; zoon, animal). They 
include fresh water hydra, marine hydroids, small jelly 
fishes (Gonionemus), and some stony corals. 

Class II. Scyphozoa (Gr. skuphos, cup; zoon^ animal). They in- 
clude most of the large jelly fishes (Aurelia). 

Class III. Anthozoa or Actinozoa (Gr. anthos, a flower; zoon, 
animal). Include sea anemones, most stony corals, sea 
fans, sea pens. 

Characteristics 

1. Radially symmetrical. 

2. They have two cellular layers, ectoderm and endoderm, with a 

non-cellular mesoglea, a jelly-like substance, between. 

3. They have a hollow body, the central space being called the 

gastro vascular cavity or coelenteron. This may be very 
small (Aurelia). 

4. They have stinging cells or nematocysts. 

Natural History 

Class I. Hydrozoa. Hydra. (Figure 21.) — Because it is so 
easy to collect and keep in the laboratory, many zoologists include 
Hydra in the first course in zoology. It is from 1/16 of an inch to 
3/4 of an inch long, and lives in fresh water attached by one end, but 
is able to move about. The body is a tube cylindrical in shape, with 

54 



COELENTERATA 



55 



a basal disk for attachment, and a ?nouth surrounded hy Jive to ten 
tentacles at the other. 

Reproduction. — Buds appear laterally, and during the repro- 
ductive season in October the spermaries (testes) may be seen on 
the anterior third of the body, while the ovaries are seen on the 
posterior or basal end. Hydra eggs resemble an ameba in ap- 
pearance. Buds are formed 
by the outgrowth of the endo- 
derm and the ectoderm, and at 
first include an enteron connec- 
tion with that of the parent. 

The outside of the Hydra, 
except the basal disc, is cov- 
ered by a thin cuticle. Hydra 
has two distinct cellular lay- 
ers, an outer ectoderm, which 
is thin and colorless, and an 
inner layer, the endoderm, 
which is more than twice as 
thick as the outer layer and 
has in it brown or green color- 
ing matter depending on the 
species. Between the ecto- 
derm and endoderm there is 
a jelly-like substance called 

the mesozlea. The body and t- it j • -j- l • 

"^ ■' ^IG. 21. hydra vtriats, showing testes 

the tentacles are hollow, the above and ovaries below. (After Hertwig- 
space being called the gastro- Kingsley, Manual of Zoology. Courtesy of 
vascular cavity or cloaca. Henry Holt & Co.) 
(Figure 22, A, B, C.) 

The ectoderm, protective and sensory, consists of (a) epithelio- 
muscular cells, inverted cones with contractile fibrils; (b) interstitial 
cells, which produce three kinds of nematocysts, (i) barbed with 
hypnotoxin; (2) cylindrical, with a coiled thread and no barbs, and 
(3) spherical, with a barbless thread in coils; (c) glandular cells at 
the basal disk, which aid in attachment. The sex cells of both 
ovaries and spermaries are derived from ectodermal interstitial 
cells. The mesoglea is thin, jelly-like and non-cellular. The 
endoderm has large digestive cells with muscle fibrils at the base, 
and with flagellae or pseudopodia projecting into the cloaca; 




56 



COELENTERATA 



absorptive cells in the gastrovascular endoderm, and secretory cells 
which are small gland cells. 




Flacjellum 



—ip if —Pseudopoc/ium 



Fig. ^iA. Hydra, longitudinal section. (Modified from Parker. Courtesy of The 

Macmillan Co.) 

Nerve cells are present in hydra in the ectoderm, a few in the 
endoderm. Some nerve cells are connected by processes with the 
muscle fibers of the epitheliomuscular cells. 



COELENTERATA 



57 



Ingestion and Digestion.— Yiydrz. feeds on those minute animals 
that it can seize with its tentacles. It attacks them with nemato- 
cysts and propels them to its mouth by tentacles. Muscular 
contraction of the body walls forces the food into the lower part 
of the coelenteric chamber. Some of the endoderm cells have 
^ro]ect\ng pseudopodia or flagella, while others are glandular. 

Digestion. — i. The secretory cells of the endoderm 
furnish the digestive fluid which acts on the contents 
of the gastrovascular cavity. 2. The digestive cells 
with pseudopodia engulf some of the food. 3. The 
absorptive cells take it in. 

Nervous Systejn. — Ectodermal nerve fibers and 
cells form a plexus. There are superficial 
cells. Some nerve cells connected with epithc 
muscular cells are motor. There are a few endo- 
dermal nerve cells also. 

Behavior. — Hydra attach, swing and 
feed, and sometimes loop or somersault. 
In response to mechanical stimula- 
tion, hydra contracts at 
first but, becoming ha- 
bituated, gives no fur- 
ther reaction, except as 
it may at times move 
away from the occupied 
region. The righting 
position is not deter- 
mined in hydra by grav- 
ity. It reacts to light, 
temperature and chemi- 
cal stimuli. I n other 
coelenterates, particu- 
larlv the sea anemones, one finds remarkable response to tactile 
and photic stimuli. 

Food. — The food of hydra consists of aquatic forms, including 
an occasional mosquito larva and rarely the eggs and fry of fishes. 

Ene?nies. — The chief enemies of hydra are bacteria, saprolegnia, 
aquatic insects and of course fishes and crayfish. 

Economic Importance. — Hydra is to some extent beneficial in 
that it captures an occasional mosquito larva. Since it also devours 




Fig. 225. Hydra stinging cells. (After Dahlgren 
and Kepner. Courtesy of The Macmillan Co.) 



58 



COELENTERATA 



annelids and Crustacea that are food for fishes it may be considered 
injurious. Gudger has called attention to early studies of Trembley 
and the more recent ones of Beardsley which indicate the surprising 
ability of hydra to capture young fishes. Beardsley found that in 
one of the hatcheries of the U. S. B. P., hydras averaged 131 per 
square inch in certain troughs used for black-spotted trout fry and 
that they were responsible for a considerable mortality among the 
young trout. 




—Endoderm 

Mesoglea 

— Ectoderm 



Fig. 22C. Hydra, cross section. (After Marshall and Hurst.) 



The Hydrozoa are especially interesting to us on account of their 
two forms of zooids, the nutritive hydranths and the reproductive 
zooids, called medusae. In many of the Hydrozoa we find alterna- 
tion of generations, the asexual generation being a fixed, plant-like 
colony, while the sexual generation is a free swimming medusa. 

Obelia, a Hydroid. — Since alternation of generations is especially 
well shown in Obelia, it is frequently used in elementary zoology 
courses. 

Obelia is a colonial animal that looks like a plant. It has a basal 
root, the hydrorhiza, attached to rocks, wharves and to alga, which 
gives off stems, the hydrocauli. The side branches from the hydro- 
cauli develop hydranths, or independent zooids, like a hydra in 
structure. The tentacles of the hydroid are not hollow but solid. 



COELENTERATA 



59 



Occasionally one finds a modified hydranth which is for the purpose 
of reproduction, and is called the gonangium. 

The perisarc is the thick outside covering, which is hard and 
chitinous. It is expanded to form the cup of the hydranth and is 
then called the hydrotheca^ or in the case of the gonangium^ the 
gonotheca. A shelf across the base of the hydrotheca is the support 




Fig. 23. Alternation of generations in the //>'^ro/iO/^f//«. (From Shumway, Gf wra/ 
Biology. Courtesy of John Wiley & Sons.) 



for the hydranth. The soft parts of the stem are called the coenos- 
arc, and the cavities of the coenosarc open into the hydranth forming 
the typical gastrovascular cavity. 

The ectoderm contains nerve cells, epitheliomuscular cells and 
interstitial cells with nematocysts of two or more types. The 
mesoglea is an undifferentiated, jelly-like layer between the ectoderm 



6o 



COELENTERATA 



and endoderm. The endoderm contains large feeding cells with 
pseudopodia and flagella, digestive cells (gland cells), and muscle 
fibers. (Figure 23.) 




Fig. 24. Portuguese man-of-war, Physalia, sheltering several shepherd fish, Nomeus, 
amid its tentacles. (Courtesy of American Museum of Natural History.) 



Alternation of Generations {Metagenesis) in the Hydrozoa. — 

In Obelia, there are two types of zooid. The reproductive one, called 
the gonangium^ produces ectodermal medusa-buds along the blasto- 



COELENTERATA 6i 

style^ which Is a continuation of the living central portion, the 
coenosarc. The medusa buds, when mature, pass out at the top 
of the gonangium and develop into medusae. Some medusae pro- 
duce eggs and some produce sperms. The fertilized eggs develop 
into a motile stage which, after swimming around for a time, settles 
down and grows into a colony similar to the parent. The colonial 
form reproduces asexually, by budding, and the medusae reproduce 
sexually, by eggs and sperms. The zoophyte stage begins in the 
autumn, and the medusa stage in the spring, so the life history takes 
one year. 

Siphonophora. — While we cannot discuss all the Orders of 
Hydrozoa, we will consider briefly one of the most beautiful of the 
pelagic forms, belonging to the Order Siphonophora. The familiar 
" Portuguese Man of War " (Figure 24) consists of a colony of 
individuals illustrating the condition of polymorphism. The 
ectoderm invaginates and produces a large pneumatophore or float. 
From the coenosarc arise individuals functioning as sensory polyps 
or feelers, and numerous retractile tentacles supplied with nettle 
cells. Feeding tubes digest and distribute the food. Reproductive 
zooids are also present. 

Class 2. Scyphozoa. — All Scyphozoa are marine, the majority 
being pelagic, i.e., swimming at the surface of the ocean. Some of 
them are beautifully colored, and certain species are phosphorescent. 
All jellyfishes are carnivorous, and the larger forms are able to 
capture and consume fishes. In their life history alternation of 
generations is found, but the asexual stage is not highly developed 
and in some cases a simple metamorphosis occurs. 

Type of the Group — Aurelia. (Figure 25.) External Char- 
acteristics. — Aurelia is a saucer-shaped jelly fish about 4 inches in 
diameter, with four distinctive gastric pouches, conspicuous because 
of the orange gonads found inside them arranged along the outer 
wall towards the margin. The concavo-convex umbrella has an 
exumbrella only slightly elevated in comparison with Gonionemus, 
and the velum is absent. Each gastric pouch has a subgenital pit. 
These have no connection with the extrusion of embryos and prob- 
ably are respiratory and excretory. 

Digestive System. — The mouth, rectangular when distended. Is 
usually collapsed In the preserved specimen. Four oral arms, folded 
like a leaf, and although they are devoid of tentacles, plentifully 
supplied with nematocysts, are used to transport food to the mouth, 



62 



COELENTERATA 



and with the aid of the nematocysts on the jnarginal tentacles^ to 
kill it preparatory to digestion. From the mouth leads a short 
gullet, situated on the 7nanubrium. The stomach is extended at 
four points into the horseshoe-shaped gastric pouches. These have 
relatively thick jelly walls. The gastric pouches have many gastric 

filaments^ covered with nem- 
atocysts, so that even if prey 
remains alive up to that point, 
it can be killed. 

The radial canals carrying 
food to the circular canal are 
of two types, the unbranched 
adradial, which proceed di- 
rectly from the sides of the 
gastric pouches to the circular 
canal, and which have no 
sense organs at their ends; and 
the branched canals, called 
per-radial and inter-radial. 
The per-radial canals orig- 
inate at the corners of the 




Fig. 25. Aurelia, a Scyphozon. (From 
Verrill.) 



mouth, between the pouches, and have a sense organ at the end 
of their central trunk; the inter-radial canals branch so close 
to the gastric pouches that one cannot in some cases actually see 
the beginning of the lateral branching. They arise at the middle 
of the outer margin of the gastric pouches, and they also have sense 
organs at the end of the main trunk. 

Respiration is osmotic through the entire animal; and possibly 
facilitated by means of the subgenital pit. Circulation is not 
vascular, merely by water currents with food in suspension. Ex- 
cretion is by the extrusion of solids through the mouth, and by 
osmosis. Again the subgenital pits may function. The circular 
canal of some medusae communicates with the exterior by small 
excretory pores at the tips of papillae. These apparently function 
in the excretion of nitrogenous wastes. 

Reproduction. — The gonads are situated in the gastric pouches 
and the eggs or sperms are discharged, not through the subgenital 
pits, but into the stomach and out through the mouth. Fertilized 
eggs are frequently seen developing attached to the oral arms. 
(Figure 26.) 



COELENTERATA 



63 



Nervous System and Sense Organs. — The nervous system consists 
of a plexus of nerve fibers extending over the subumbrellar surface 
between the epithelial layer of ectoderm and the muscular layer. 
The plexus is thickened in a ring extending around the animal near 
the circular canal and connecting with the sense organs, or tentaculo- 
cysts. The marginal tentaculocysts are equilibratory and olfacto- 
gustatory. Adjacent to the ocellus or statocyst are found the so- 
called " olfactory pits." 




Fig. 26. Development oi Aurelia. First row, growth of planula to scyphostoma; 
below, strobilation (separation of ephyrae): left, oral view of scyphostoma; right, two 
ephyrae. (After Hertwig-Kingsley, Manual oj Zoology, after Hatschek. Courtesy of 
Henry Holt & Co.) 



Class 3. Actinozoa (Anthozoa). Sea Anemone. — The Actino- 
zoa include numerous species of sea anemones and corals. Sea 
anemones are solitary animals, forming no permanent colony. 
They are fleshy, with no skeleton. 

Anatomy of the Sea Anemone. — The sea anemone is cylindrical, 
with xx.^ peristome covered with hollow, horn-shaped tentacles, bear- 
ing nematocysts. The mouth is provided with a muscular ciliated 
groove, the siphonoglyph, which aids in holding and propelling the 
food. George Meredith said, " Sea anemones are flowering stomachs 
which open to anything and speedily cast out what they cannot con- 



64 



COELENTERATA 



sume." The gastrovascular cavity is divided by thin double mesen- 
teries into six radial chambers. Other shorter mesenteries, not at- 
tached to the digestive tube, incompletely divide the cavities still 
further. Near the base of the coelenteric chamber (gastrovascular 
cavity) there are two types of mesenterial filaments. The first are 
secretory in function, while the second, the acontia^ are provided with 
gland cells and nematocysts. The acontia may be shot out through 
the body wall of an irritated anemone until the mass of white threads 
conceals the bottom of an aquarium jar. Italians eat certain sea 
anemones, terming them " ogliole." 




Fig. 27, Corals. (Courtesy of American Museum of Natural History.) 

Corals. — The coral polyps resemble the sea anemones in their 
internal structure, having an esophageal tube, mesenteries, and 
internal gonads. Unlike the anemones, they form colonies^ and have 
leathery, calcareous, stony, or horny skeletons of ectodermal origin. 
In the red coral, originally separate spicules become embedded 
in a cement-like deposit of calcium carbonate, forming a hard 
branched rod which serves as an axis for the colony. Members of a 
coral colony are connected, each individual securing its own food. 



COELENTERATA 



65 



however. In one group of stony corals, the zooids are differen- 
tiated, certain smaller individuals, the siphonozooids, lacking 
longitudinal muscles, tentacles and gonads. Red coral is fashioned 
into jewelry for children, while the white and rose pink Japanese 
corals bring high prices. (See page 70.) 

The living polyps are significant since they may become the 
foundation of islands, or protective barrier reefs (Figure 28), but 
frequently menace shipping when they grow to a point just below 




Fig. 28. Great Barrier Reef of Australia. (Courtesy of Amer. Mus. of Nat. Hist.) 

the surface. In general, the corals that build reefs are found in a 
zone extending about 30° on each side of the equator. For the 
most part, since they cannot live in water below a temperature of 
about 60°, corals are found in tropical waters, near the coast, ranging 
no lower than 20 fathoms, and never found in brackish or fresh water. 
Formation of Coral Islands. — Charles Darwin suggested that an 
island surrounded by a coral reef might subside,^ thus accounting 
for an atoll and its enclosed lagoon. (See Figure 29.) Sir John 
Murray and A. Agassiz have staunchly supported the erosion theory. 
According to this theory coral reefs form around an oceanic island. 
The reef grows but the soil and rock of the island are washed away 
until an atoll with its lagoon are left. The few lagoons that serve 

^ Davis, W. M., 1928, in his book The Coral Reef Problem, Am. Geog. Soc, agrees 
with Darwin. The glacial control theory of Daly is the only serious rival to the sub- 
sidence theory. 



66 



COELENTERATA 



as safe harbors for ships do not offset the many dangerous coral 
reefs that threaten ocean shipping. 




Fig. 29. Whitsunday Island in the South Pacific, an atoll built by corals. (After 

Darwin.) 

Ctenophora. — The Ctenophora (Gr. ktenos, of a comb; phoreo, I 
bear) are free-swimming marine animals, extremely transparent, 
and for the most part found in tropical seas, although quite gen- 
erally distributed. They are called sea walnuts or comb jellies. 

(Figure 30.) 

They are of little importance 
except as food for other marine 
animals. The U. S. Bureau of 
Fisheries has, however, reported the 
appearance of great numbers of 
Ctenophores coincident with the 
disappearance of oyster larvae in 
Great South Bay. Formerly known 
as destructive to molluscan larvae, 
there have been a number of years, 
1917, 1921, 1927, when heavy 
" sets " of young oysters were lost 
during the month of June. Prob- 
ably certain temperature conditions 
were responsible for the appearance 
of the Ctenophores at a date earlier 
than usual, and at a time when they could do damage to young 
oysters. It is of course also barely possible that the temperature 
changes were injurious to the oysters, and that the injury done by 
Ctenophores was correspondingly less. 




Fig. 30. Mnemiopsis, a Ctenophore 
(Courtesy of T. C, Nelson.) 



COELENTERATA 67 

General Consideration of the Coelenterata 

Distribution. — The majority of the Coelenterates are found in 
salt water, where they are extremely numerous. The common 
fresh water hydra and a species of fresh water medusa are the only 
inland types. 

Anatomy. — All Coelenterates have a body wall consisting of two 
layers of cells (ectoderm and entoderm) and an undifferentiated 
mesoglea. Digestion and circulation take place in a single coe- 
lenteron. Muscle fibers aid in the process of locomotion. Loco- 
motion is active in the jelly fishes like Gonionemus, which ejects 
jets of water, but less rapid in the larger jelly fishes, which execute 
undulatory movements. Hydra loops and somersaults. 

Physiology. — Digestion is largely extracellular in some coe- 
lenterates, the enzymes being discharged into the gastrovascular 
cavity. In others it is an intracellular process. The endoderm 
cells responsible for digestion and absorption are ameboid in 
character, in some cases apparently fusing to form a syncytium. 
In many Coelenterates, cilia or flagella bring about a slow circulation 
of the liquid, which may be termed gastrovascular circulation. 
Tryptic ferments found in some Coelenterates probably furnish an 
acid secretion as in protozoa. Digestion of animals with a chitinous 
covering is effected in the anemones by mesenterial jilmnents which 
penetrate to all parts of the body and there digest and absorb food 
matters. There is little or no evidence of free existence of pro- 
teolytic enzymes in the gastral cavity. Glandular cells empty their 
secretion into the gastric cavity, where it becomes liquid and 
evidently has a part in what may be termed predigestion of food. 
Products of this early digestion may be, and doubtless are, carried 
to the most distant parts of the body by a sort of circulation, some- 
times termed gastrovascular. This group appears to present a 
sort of transition between purely intracellular digestion as it appears 
among the protozoa and purely extracellular digestion found in 
higher animals. 

Respiration and excretion are performed through the body wall 
and solid wastes are extruded through the mouth. 

Nervous System. — In the Coelenterates we find that specialized 
ectodermal cells receive and transmit stimuli to internally situated 
contractile cells. The nerve net consists of a diffuse network be- 
tween the receptor and effector cells. Parker ^ calls the units of 

^Parker, G.H. 1919. Elementary Nervous System. J. B. Lippincott Co., N. Y. 



68 COELENTERATA 

this nerve net protoneurons . There are sense organs for equilibra- 
tion, touch, visual sense and gustation. 

Reproduction is asexual, by fission and budding; and sexual, 
by ova and spermatozoa. Hermaphroditism and separate sexes 
are both found. Many species of Coelenterates give off medusae 
when not a month old. Their life cycles may be completed in three 
months. Sagartta completes its life cycle in about 15 months. The 
sea anemones may undergo pedal " laceration," which is asexual 
reproduction. 

Size. — Hydrozoa are mostly of small size. The Scyphozoan 
jelly fishes are larger, Cyanea arctica reaching a diameter of 12 feet 
with tentacles nearly 100 feet long. The largest reef anemone, 
Discoso?na, an Actinozoan found in the Mediterranean Sea, reaches 
a diameter of 1 feet. 

Habitat. — A little hydroid lives in the mouth of the tube of the 
worm Sabella. Stylactis^ another hydroid, lives on the skin of the 
rock perch, Minous minot. Stylactis vertnicola attaches to the worm 
Aphrodite at 2,900 fathoms. Scyphozoa have been found at a 
depth of 2,000 fathoms. 

Regeneration. — The remarkable ability of Hydra to regenerate 
has been known since the experimental work of Trembley in 1744. 
The hypostome with the tentacles will produce an entire new Indi- 
vidual, and as many as seven heads have been produced by splitting 
the animal anteriorly. Hydra may be turned Inside out and become 
normal in a short time. It was at first thought that the ectoderm 
cells were transformed into endoderm. This Is not so, however. 
The animal either turns Itself back or else the inturned ectoderm 
disappears and new ectoderm forms from the lips downward, cover- 
ing the endoderm. 

Interesting experimental work has been done by several investi- 
gators with various Scyphozoa Including Aurella. They regenerate 
remarkably when segments are cut out. 

Fossil Relatives. — Hydrozoa are found as fossils from the Cam- 
brian to the present. Scyphozoa are 99 per cent water and so few 
traces remain In the rocks. Lithographic slates, found In the Juras- 
sic strata of Bavaria, show the impressions of the thin soft bodies 
or tentacles of jelly fishes. Sometimes the digestive cavity was 
filled with sand and covered by other mud or sand before the body 
of the jelly fish disintegrated and so the outline of the containing 
cavity was preserved. Actinozoa or Anthozoa are found from the 



COELENTERATA 69 

Cambrian to the present. Corals are composed of CaCOa and so 
are well preserved. Sea anemones and Ctenophores are not 
preserved as fossils. 

Ancestry and Relationship to Other Phyla. — The lowest Coe- 
lenterate form known is the simple hydrozoan polyp, represented by 
Hydra and by the hydrula stage of many Hydrozoa. Scyphozoan 
polyps are represented by the scyphula of Aurelia, which is more 
complex because of the stomodaeum, gastric ridges and filaments. 
The Actinozoan polyp or actinula is more complex still. 

The hydroids have adopted asexual multiplication by budding 
during the larval stage. Certain of the zooids become medusae^ the 
rest retaining the polyp form and furnishing nourishment for the 
asexual colony. 

The relationships of the Ctenophora to other Coelenterata are 
doubtful. While the absence of stinging capsules and the presence 
of collared endoderm cells in the Porifera places them in a separate 
Phylum, it is assumed that they were derived from the Protozoan 
ancestors of the Coelenterates. 

Economic Importance of Coelenterates 

Hydrozoa. — Hydra is an enemy of mosquito and other insect 
larvae, but of relatively small importance in such a role. It also 
attacks trout fry. Hydra is an enemy of annelids {Tubifex) and 
small Crustacea such as Daphnia, which are important food for 
fishes. The hydroids are food for fishes. Polypodium is in early life 
parasitic on the eggs of the sturgeon. Scyphozoa are eaten in Japan 
and the Philippines, preserved in salt or between oak leaves. 
Sertularia are sometimes sold as " air-plants." 

Actinozoa. — Sea anemones have been used as food by the Italians 
for many years. They are sold under the name of " ogliole." 
When fried in oil they are said to be very palatable. In the West 
Indies, a coral-like form called the " sea-ginger " is esteemed as a 
condiment. 

Corals are the only Coelenterates of great importance economi- 
cally. Coral reefs are formed by the limestone secretions of in- 
numerable animals resembling anemones somewhat in structure. 
Sometimes reefs of coral surround islands which submerge (Darwin's 
theory, page G^) and leave a " lagoon " that proves a safe haven 
for ships. But, in many cases, reefs are dangerous liabilities in 



70 COELENTERATA 

ocean travel. Many Pacific Islands are formed entirely of coral 
rock, while the East Coast of Northern Queensland is bounded for 
1,250 miles by the Great Barrier Reef, which extends parallel to the 
coast at a distance from shore ranging from 10 to 90 miles. (See 
page 65.) 

The precious corals have been known for centuries. In India, 
coral is used as a gift to the dead to keep evil spirits away from the 
bodies. Pure white Japanese coral necklaces are extremely valu- 
able, those with pale pink tints bringing as much as $5,000. The 
finest rose-pink coral brings from $400 to $600 an ounce, but the 
ordinary red pieces bring only about $10. The small fragments used 
in children's necklaces bring about ^oi. a string. 

References on Coelenterates 

Hargitt, C. W. 1 901. Synopsis of the Hydromedusae of North 
America. American Naturalist, vol. XXXV. 

Trembley, a. 1744. Memoires pour servir a I'histoire d'un genre de 
polypes d'eau douce a bras en forme de cornes. Leyden. (Re- 
markable first study of Hydra.) 



CHAPTER V 

Platyhelminthes 

The Platyhelminthes (Gr. plains, broad; helminthus, an intes- 
tinal worm) are soft bodied, bilaterally symmetrical and dorsi- 
ventrally flattened worms lacking the true segmentation character- 
istic of the earthworm. The majority of the Turbellaria are free 
living, the Trematodes are all ectoparasites or endoparasites, and 
the Cestodes are all endoparasitic. Some parasitic flatworms re- 
quire several hosts in order to complete their life history. 

Platyhelminthes have two embryonic layers, the ectoderm and 
endoderm. They differ from higher worms in that they have no 
coelom. A packing tissue, the mesenchyme, forms a compact mass 
oi pa7-enchyma (connective tissue) occupying the space between the 
organs and the body wall. The majority are hermaphroditic, i.e., 
with the gonads of both sexes in one individual. The digestive 
tract, when present, is a coelenteron with no anal opening. 

Classification 

Class 1. Turbellaria (Lat. turbo, I disturb), Planaria. 

Class 2. Trematoda (Gr. trema, a pore; eidos, resemblance), 

Distomes, liver flukes. 
Class 3. Cestoda (Gr. kestos, girdle; eidos^ resemblance), tape 

worms. 

Characteristics 

I. Flattened dorsiventrally. 
1. Bilaterally symmetrical. 

3. Do not bud to form a colony, but do form linear chains (tape 

worm). 

4. Lack a coelom, the spaces between the organs and body wall 

being occupied by connective tissue called parenchyma. 

5. Excretory system of paired branched proto-nephridia or flame 

cells, connected in a water vascular system. 

6. Nervous system consists of a supra-esophageal ganglion with main 

ventral nerve trunks. 

7. Have two embryonic layers. 

71 



72 



PLATYHELMINTHES 



Natural History 

Class I. Turbellaria. — Turbellaria are unsegmented worms, 
living in fresh, brackish or salt water or moist earth. They are 
elongated and flat, and antero-posteriorly differentiated, with two 
prominent eyes. They vary in color from transparent to red, gray, 
brown and almost black. Some {Planaria maculatd) are spotted. 
Locomotion is by undulation and by means of cilia. (Figure 31.) 



5ra/n 

Eye 
■ Ovory 

YolR (glands 



In^esfine 




-Lofero/ nerve 



Vos deferens- 



Genital pore' 



1- Pharynx 

~Infes//'ne 

■ Mouth 
Penis 



Oviduct 
Vocjina 



Fig. 31. A Planarlan worm. (From Lankester, after von Graff.) 



Planarians vary in size, but do not usually exceed one-half inch 
in length. Some greenhouse and tropical tree planarians are over a 
meter in length. They are widely distributed in fresh or salt water, 
but only a few are pelagic. They usually live free but are sometimes 
found in a state of commensalism, as for example Bdelloura, which 
lives in the gill books of the horseshoe crab, Limidus. Planaria are 
dorsiventrally differentiated and have eye-spots and ganglia. The 
lappets, antero-laterally situated, are olfacto-gustatory organs. 
The ectoderm is ciliated, often glandular, and equipped with rhab- 
dites, rod-like bodies capable of being discharged on irritation. 
Turbellaria with a branched digestive tract are called Dendrocoela, 
and those with a straight digestive tract are called Rhabdocoela. 



PLATYHELMINTHES 73 

Type of Group — Planaria. Anatomy of P. maculata. — The body- 
wall consists of the ciliated epidermis basement membrane, circular 
muscles, external longitudinal muscles, internal longitudinal mus- 
cles, outside of the connective or packing tissue, called parenchyma. 

Digestive System. — The mouth is situated at the end of a pro- 
trusible proboscis or pharynx, which is midventral. The mouth 
leads into a central tube which may be axial as in the Rhabdocoela, 
or branch, one running towards the head, and two, postero-laterally, 
towards the tail. Digestion is both intercellular and intracellular. 
Irregular columnar cells and goblet cells line the digestive cavity. 
The goblet cells secrete an enzyme, probably used entirely in the 
digestion oi fat. Intracellular digestion begins when the columnar 
cells push out pseudopodia which seize and ingest food particles, 
which later appear in vacuoles. There is no anal opening and any 
undigested food must be discharged from the mouth. 

There are no well-developed circulatory or respiratory systems, 
as the branched digestive tract distributes the food in the form of 
lymph. 

Excretory System. — The water vessels of the excretory system 
run through all parts of the body. They consist of two main 
longitudinal trunks running on the right and left sides of the body 
and opening externally on the dorsal surface by means of several 
minute pores; connected in front by a transverse vessel. From 
each main trunk come numerous branches which give off in turn a 
system of fine vessels which terminate in flame cells, which are cells 
with cilia directed down the tube. Some zoologists think that they 
may also be respiratory in function. 

Reproductive System. — The reproductive system is hermaphroditic 
(monoecious). The male part of the apparatus consists of the 
testes., vasa deferentia and cirrus or penis. The testes are numerous, 
rounded structures situated near the right and left borders. Two 
ducts, the vasa deferentia, run backwards from the neighborhood 
of the testes and unite in the middle line posteriorly. The median 
duct thus formed passes into the protrusible cirrus which opens in 
the genital cloaca. At the base of the penis the seminal vesicles 
empty, while the ducts of the prostate glands also empty into the 
canal. The female reproductive organs consist of the ovaries, 
oviducts, vitelline glands {yolk glands) and the uterus, a muscular sac. 
Fertilization takes place in the uterus and the eggs develop in cocoons 
that are passed along the oviducts from the animal's body, producing 



74 PLATYHELMINTHES 

tremendous lacerations sometimes, but the tissue destroyed is 
easily regenerated. 

The cocoons contain about a score of eggs with several hundred 
yolk cells containing food. The larva at a certain stage develops a 
temporary larval mouth and gullet, and swallows the food yolk, 
by which it is able to grow rapidly. The larval mouth disappears 
and a new permanent mouth replaces it. The embryo is like its 
parents when it leaves the shell. Adult over-nourished Planaria 
undergo fission, the posterior portion quickly regenerating a head. 

The nervous systejn consists of the brain, a bilobed affair with two 
longitudinal nerve cords or ventral nerve chains running backwards, 
and giving off, internally and externally, transverse branches which 
also subdivide. The inner ones frequently anastomose to form 
commissures. The brain is rather diffuse and made up of groups of 
ganglion cells, nerves, and has transverse fibers connecting the nerve 
cords. The animals are responsive to all sorts of stimuli, and the 
eye-spots, the lateral olfacto-gustatory organs, and the anterior end 
are all well supplied with nerve endings. 

Food. — Planaria live upon small Crustacea, larvae of Crus- 
tacea, water mites, and Rotifera, as well as on plant food such as 
diatoms and algae. They are also said to attack earthworms. 

Class 2. Trematoda. — The Trematoda are leaf-like parasites 
with no cilia in the adult, a thick cuticle, ventral suckers, sometimes 
with posterior hooks, and with a forked or branched alimentary canal 
ending in blind branches, the cecae. 

Type of Group. — The liver fluke, Fasciola {Distomum) hepatic a. 
The adult liver fluke lives in the bile ducts of sheep, cattle, horses 
and pigs, and sometimes occurs in man. It is soft-bodied, flatteneft 
and leaf-like with a triangular lobe at the broader end, and with two 
well-developed suckers, the anterior one being perforated by the 
mouth, and the posterior one ventrally situated. The disease 
" liver rot," which is especially prevalent among sheep pastured on 
snail-inhabited marshy ground, has killed many millions of sheep. 

Life History. — The eggs of the liver fluke are 1/180 of an inch 
long, with brownish shells, having a greenish sheen. They can 
develop only in water where they hatch in from four to five weeks. 

The larva or miracidium is 1/125 of an inch long, ciliated, and 
with a single eye, but has no gut. If the larva does not find a 
snail of the right species in from eight to ten hours, it dies. Having 
entered the lungs of the snail, it loses its cilia, becomes broader and, 



PLATYHELMINTHES 



75 




Fig. 32. Life-history of Fasciola hepatica. A, "egg"; B, miracidium; C, sporo- 
cyst; D, E, rediae; F, cercaria; G, tail-less encysted stage; E, adult (neither reproduc- 
tive organs nor nervous system is shown), b.o. Reproductive opening of redia; c, 
cercaria; E, egg; ent, intestine; g, nerve-ganglion; g.c, germ-cells; g.l, cyst-producing 
gland-cells; n, nephridium (only a few of the main branches of the excretory network 
are shown); n.o, nephridial opening; o.s, oral sucker; p, proboscis (extruded); v.s, 
ventral sucker; y, yolk-cells. (After Kerr. Courtesy of Macmillan and Co., Ltd.) 



76 



PLATYHELMINTHES 



as a sporocysty develops germ cells which produce embryos. These 
embryos grow into rediae which have germ cells and a primitive 
digestive tube including a mouth, a pharynx and an intestine but no 
anus. If the weather is warm, the rediae continue to multiply in 
the lungs of the snail. If it is cold they multiply for a short time 
and then pass into the liver of the snail where they give rise to tailed 
forms called cercariae which have an oral and a ventral sucker, and 
a forked intestine with no anus. The cercariae escape from the 



P'e-nis ~--.^ 



Ovary 



Shell (j/and 



Vas c/eferens 




''rot sucker 



Uterus 



Vas deferens 



- Yolk-duct 



Testis 



Yolk-qlonc/s- 



Fig. 22- -A" adult liver fluke. (After Kerr. Courtesy of Macmillan and Co., Ltd.) 



body of the snail and, after swimming about, settle down on grass, 
later becoming encysted. When their plant substrate is eaten the 
cercariae develop in about six weeks into adult liver flukes and travel 
from the intestine of the sheep to its bile ducts. Thus from one 
single egg come the larval stages, miracidia, sporocysts, rediae^ 
cercariae and finally many adult flukes. 

The adult liver fluke is a tailless cere aria with well-developed 



PLATYHELxMINTHES 77 

hermaphroditic gonads. Its digestive system consists of a mouth, 
pharynx, oesophagus, intestine and non-anastomosing caecal tubes. 
The intestine is usually darkened by the blood and bile used as food. 
The excretory syste?n consists of a main duct with four anterior ducts, 
a dorsal and a ventral one on either side. The nervous system 
consists of a collar around the pharynx; two lateral ganglia and one 
ventral median ganglion. The male reproductive system consists of a 
pair of testes, vasa deferentia near the seminal vesicle, the ejacu- 
latory duct and the penis or cirrus with its sac. Tho. female repro- 
ductive system consists of the ovary, oviduct, yolk glands, shell gland, 
vitellarian ducts and the vagina or uterus, opening at the genital pore. 

Trematode Parasites.— Some of the trematodes infesting other 
mammalian hosts are likely to infest man occasionally. For exam- 
ple, Fasciola hepatica has been found in the human liver. Some 
are normally parasites of man. 

The blood fluke Schistosojna (Bilharzia) haojiatobium is a human 
parasite found in Egypt involving large numbers of troops during 
the recent war. The cercaria enter the blood stream through the 
skin, finding their way to the small veins of the bladder and colon 
and becoming mature in the submucous tissue. They require as an 
intermediate host the non-operculate fresh water snail Bulinus or 
Planorbis. Developing in the liver of the snail into tubular sporo- 
cysts, germ cells develop within the sporocysts into cercariae with 
forked tails. These later escape from the snail and in the free state 
these cercaria must find a mammalian host in forty hours or die. 
When they come in contact with mammalian skin they cast off their 
tails, dissolve the cells of the skin, and work their way into a lym- 
phatic or the blood stream and thence to the liver where they 
mature and eventually lodge in the mesenteric veins. There was 
very good scientific basis for the blind worship of the Nile ibis, an 
important enemy of snails. (See p. 154.) 

Schistosoma japonicumy found in the Orient, is somewhat smaller 
than Bilharzia. It requires as its intermediate host the snail 
Katayama nosophora in Japan and Oncomelania hupensis in the 
Yangtze Valley. It is quite possible that several snails found in the 
United States might act as carriers for Schistosoyna japonicum but 
none as yet have been found. Schistosoma cause inflammation of 
the rectum and bladder. Other species of Schistosoma ^ are found 
in tropical America, the West Indies and the Philippines. 

3 Cort, W. W. 1928. Schistosome dermatitis in the United States (Michigan). 
Jour. Amer. Med. Assoc, vol. 90, p. 1027. 



78 



PLATYHELMINTHES 



Clonorchis sinensis^ found in China and Japan and recently- 
introduced into the U. S., infests the liver of man, cats, dogs and 
pigs. It is generally leaf-like in shape and has two suckers. The 
eggs hatch in the operculate snail Bithynia and the cercariae leave 
the snail and encyst in thirty-four reported species of fresh water fish. 
Man and the other mammalian hosts acquire the infection by 
eating uncooked infected fish. 




Fig. 34. Cercaria and adult of Cryptocotyk lingua. (Courtesy of H. W. Stunkard.) 

In Cryptocotyle lingua., studied by Stunkard,-* we have an in- 
teresting illustration of what may occur with introduced species. 
The snail, Littorina litto?-ea, brought with ballast to New Brunswick, 
Canada, in 1855, is supposed to have carried with it the cercariae of 
Cryptocotyle lingua. The metacercariae of C. lingua occur in 
marine fishes, chiefly the cunner, and adults are found in the intes- 
tines of fish-eating birds and mammals. Four related species have 
been shown experimentally to be infective for man. (Figure 34.) 
It is possible that this form, readily collected at the Marine Biologi- 
cal Laboratory, Woods Hole, Mass., may be used inland just as the 
nematode Metoncholaimus pristiurus is now being shipped to dis- 
tant points. (See page 98.) 

Class 3. Cestoda. Type — Taenia solium. — The common pork 
tape worm lives in the alimentary canal of man as an adult. Its 
secondary host is the pig. The adult tape worm has a well-developed 

* Stunkard, H. W. 1930. The life history of Cryptocotyle lingua. Jour. Morph. 
and Physiol., vol. 50, pp. 143-183. 



PLATYHELMINTHES 



79 



" head " or scolex armed with both hooks and suckers. The pro- 
glottids are budded from the neck, the oldest being at the posterior 
end. The worm may reach a length of over twelve feet and have 
1,000 proglottids. 

An alimentary canal is not necessary on account of the parasitic 
habit of absorbing food predigested. Excretory tubes end in flame 
cells. 

The complete reproductive system develops in each of the pro- 
glottids and attains sexual maturity beginning with the 200th. 
The animal is male nearer the anterior end and hermaphroditic 
posteriorly. The male structures consist of testes, efferent ducts, 
vasa deferentia, a cirrus and a cirrus sac. 

The female reproductive system consists of the paired ovary, 
the oviduct, yolk gland and duct, shell gland and duct and the uterus 
and vagina. The uterus is simple until the 600th segment; then it 
branches. 

The egg rises in the ovary, passes into the oviduct, and is included 
with the yolk cells and spermatozoa in a chitinous shell, and finally 
passes into the uterus and is released by rupture of the uterus when 
the matured segment is discharged. Fertilization takes place before 
the shell is formed, and may be by sperms from the same proglottid. 
The eggs develop into hexacanth (6 hooked) embryos while still in 
the uterus. They pass out in the feces and if eaten by a pig escape 
from their covering and bore into the muscles. A proscolex, which 
is a cyst with the cavity filled with water, develops a head and forms 
a bladder worni or cysticercus with the scolex invaginated into the 
bladder. When infested pork which is not fully cooked is eaten, 
man receives cysticerci, which evert and attach, by the scolex, to the 
wall of the alimentary canal and develop a chain oi proglottids. 

Cestode Parasites. — Echinococcus granulosus {Taenia echino- 
coccus) is found in the intestine of the dog. It is the most injurious to 
man of the parasites belonging to the Cestode group and is taken into 
the body upon unwashed salads or in drinking water contaminated by 
ova from infected dogs. The adult worm in the dog has usually not 
more than four or five proglottids. When the eggs reach the ali- 
mentary canal of man, cattle, sheep, and hogs, the egg shells are 
dissolved and the hooked embryos bore into the liver where they 
develop into cysts. The bladder-worm stage is extremely large, 
sometimes reaching a diameter of seven inches. It produces a large 
number of scolices which in turn produce other crops of scolices. 



8o PLATYHELMINTHES 

The tissues of the host wall up the bladder worm and the enlarging 
bladder worm is known as a hydatid cyst. 

Taenia saginata is a human tape worm which grows to a length 
of forty feet, its terminal segments reaching a width of 3/16 of an 
inch. The scolex has four large strong suckers without hooks. The 
cysticercus stage is found in the muscles of cattle and occasionally 
in dogs. It is more common in the United States than the pork 
tape worm. 

Taenia solium is one of the commonest tape worms of man in 
Europe. It reaches a length of twelve feet. Its scolex has both 
suckers and hooks. The " bladder worm stage" Cysticercus cel- 
lulosae, is found normally in the muscles of the pig but also occurs 
in the dog, cat, rat and man. 

Dipylidium caninum is found in the dog and cat and occasionally 
occurs in man. Each proglottid contains a double set of repro- 
ductive organs. The cysticercus is extremely small, a fact cor- 
related with its existence in secondary hosts as small as dog lice 
and fleas. 

Taenia serrata, the common tape worm of the dog, has the rabbit 
as its secondary host. If the rabbit swallows the eggs of the tape 
worm, larvae develop in the alimentary canal and bore their way 
through its wall into blood vessels which carry them to the liver. 
From the liver the larvae migrate to the peritoneal cavity where 
they grow into bladder worms or cysticerci. When a bladder worm 
is swallowed by a dog the scolex attaches to the mucous lining of the 
alimentary canal by means oi hooks and suckers and buds off a chain 
of proglottids. 

Taenia coenurus, the dog tape worm, produces larvae {Coenurus 
cerebralis) which infest the brain of cattle, sheep and deer and cause 
the disease known as " staggers " or " gid." It has many segments 
as an adult in the intestine of the dog, and the cystic form may reach 
a size of ^ of an inch in the brain of the intermediate host. 

Diphyllobothrium latum^ the broad tape worm, causes anemia in 
man. Its ciliated hexacanth embryo gets into the gut of a fresh 
v/ater copepod, Cyclops strenuus or Diaptomus gracilis, then is 
eaten by fish in whose muscles it encysts in the form of an immature 
worm known as a plerocercoid. If eaten uncooked it becomes the 
adult tape worm in man. Recently immigrants from Finland and 
Baltic regions of Europe have introduced this parasite in the Great 
Lakes region where fish have become infected. It is believed that 



PLATYHELMINTHES 



8i 



the severe anemia produced by this parasite is due to a toxin given 
off by the tape worm and absorbed into the blood of the host.^ 

Although there are many parasitic flatworms to be found in 
fishes, birds and mammals, there is little danger of contracting 
disease if the meats are well cooked.^ 




A B 

Fig. 35//. Tapeworm head, cp, cirrus pouch; gp, genital pore; n, nerve; ov, 
ovary; sg, shell gland; /, testicles; tc, transverse canal; ut, uterus; 0, vagina; vc, ventral 
canal; vd, vas deferens; vg, yolk gland. X 20. (After DefFke, 1891, pi. i, fig. 3.) 
{Coenurus cerebralis.) B. A segment. (Ranson. U. S. Dept. Ag., Bull. 66.) 



Remedies for Platyhelminth Infections. — While it has been 
demonstrated that santonin and nicotin, in doses fatal to ascarids, 
have little effect on the cestodes, we know that the tape worm, 
Taenia, is more sensitive to Beta-naphthol than Ascaris. The oil of 
" male fern " {Aspidium) and Chenopodium are specifics for tape 
worm. They stupefy the animal, it releases its scolex, and then a 
mild cathartic will remove the whole worm. 

* Vergeer, T. 1928. Dipkyllobothrium latum (Linn. 1758) the broad tapeworm 
of man. Jour. Am. Med. Assoc, vol. 90, pp. 673-678. Also consult: Lyon, M. W., Jr. 
1926. Native case of infestation by the fish tapeworm Diphyllobothrium latum. 
Jour. Am. Med. Assoc, vol. 86, pp. 264-265. 

^Linton, Ed. 1912. Cestode cysts in the flesh of marine fish and their bearing 
on food values. Trans. Am. Fish. Soc (References.) 



82 PLATYHELMINTHES 



General Considerations 



Distribution. — Free living flatworms occur from the deep sea to 
the surface of fresh water lakes, while parasitic forms infest animals 
of all the higher Phyla. 

The Turbellaria are usually free-living, consuming insect larvae 
and aquatic worms and eking out their diet by means of diatoms and 
algae. Some forms like the flatworm, Bdelloura, which lives in the 
gill books of the king crab, are commensals, while still others are 
found parasitic in the intestines of Echinoderms and worms. 

The Trematoda are all parasitic, some of them attaching to the 
gills of fishes by hooks and suckers as ectoparasites. Others are 
true internal parasites, found in the pericardial cavity of the mussels, 
the urinary bladder of Amphibia and the alimentary canals, liver 
and lungs of vertebrates. Many Trematodes find molluscs neces- 
sary as their secondary hosts, the commonest instance being that 
of the liver-fluke and the snail. 

The Cestoda are internal parasites usually found in the ali- 
mentary canal and requiring another vertebrate or invertebrate as 
a secondary host. Passage from one host to another is not an active 
migration as in the Trematodes. On account of their extreme 
parasitism we find that the Cestodes are the most degenerate of the 
flat worms. 

Physiology. — The Turbellaria are covered with fine vibratile 
cilia which aid in respiration as well as locomotion. They have a 
well-developed, branched digestive tract, and a complicated excre- 
tory system consisting of water vessels which give off fine capillaries, 
which terminate in flame cells. It is assumed that the excretory 
system may also function in respiration. The reproductive system 
is " monoecious," or hermaphroditic? The nervous system is 
highly developed, consisting of central cerebral ganglia or brain, 
from which proceed posteriorly two longitudinal ventral nerve 
cords, with connecting nerve strands or commissures. The Trema- 
toda lack cilia but have minute cuticular papillae. They have an 
anterior mouth surrounded by a muscular oral sucker, while poste- 
riorly is a larger ventral sucker. Other openings are the median 
genital openings and the posteriorly situated excretory pore. The 
mouth leads into a muscular pharynx, a short esophagus and a rather 

"^ Consult Curtis, W. C. 1902. Life history, normal fission, and reproductive 
organs of Planaria maculata. Bost. Soc. Nat. Hist., vol. 30. 



PLATYHELMINTHES 83 

large intestine which divides into two lobes, each branched into 
ceca. The only external opening of the alimentary canal is through 
the mouth. Excretory system and nervous system are well de- 
veloped, while the reproductive organs are hermaphroditic. In the 
Cestoda we find that an alimentary canal is absent, but that repro- 
ductive, nervous, and excretory systems are well developed. 

Behavior. — The Turbellaria have well-developed tactile, olfac- 
tory-gustatory and light percipient organs, but in the Trematodes 
and Cestodes little development of these functions is found. In the 
green marine worm, Convoluta roscoffensis^ geotropism has been 
found to fluctuate with the rise and fall of the tides, even when the 
animal was moved to an aquarium. Geotropism is dependent on the 
statocyst. In Convoluta and in another Turbellarian, Vortex, it is 
found that the parenchyma contains symbiotic unicellular green 
algae (see page 26) similar in relations to that with the yellow cells 
of Radiolaria. 

Regeneration. — Planaria are notable in their ability to regenerate 
new parts, a single individual having been cut into one hundred 
twenty transverse pieces, behind the eyes, and each piece regenerat- 
ing a perfect worm. The tape worms are able to produce new pro- 
glottids as long as the scolex remains. 

Fossil Relatives. — Fossil flatworms are rare. They occur from 
the Pennsylvanian down to the present. 

Ancestry and Relationship to Other Phyla. — The Turbellaria 
and the Ctenophora have possibly been derived from a common 
ancestor, the bands of cilia in larval Turbellaria resembling some- 
what the ciliary swimming plates found in Ctenophora. The 
simplest Platyhelminthes are Turbellaria; then we come to the 
Trematoda, in which the larval cercaria corresponds to the cysticerci 
of the Cestoda. The form Ligula has been considered a connecting 
link between the Trematoda and the Cestoda, since it has the 
elongated body and multiple gonads of the tape worm, but repre- 
sents only a single proglottid. 

Axial Gradient Theory of Child.— Dr. C. M. Child of the 
University of Chicago, after experimenting with Planaria for many 
years,^ elaborated an important theory of axiate organization, 
according to which there is a gradient of metabolic activity in every 

8 Consult also Child, CM. 191 5. Individuality in Organisms; and Senescence 
and Rejuvenescence. Published by Univ. of Chicago Press. 



84 PLATYHELMINTHES 

organism. Dr. Child kindly consented to prepare for this text a 
brief summary, which we are privileged to print without alteration. 

"Many different lines of evidence, observational and experimental, 
indicate that physiological polarity of axiation in general is in its simplest 
terms a gradation or gradient in physiological condition along the axis in 
question involving both quantitative differences in metabolism and proto- 
plasmic constitution. During development the primary gradient or 
gradients may be altered, may disappear and new gradients may arise so 
that the original gradients do not necessarily persist in the adult organism. 
Localization and differentiation at different levels of an axis result from 
the differences in physiological condition at different levels of a gradient 
and are often factors in altering or obliterating the original gradient. 

"The evidence also indicates that such gradients arise or originate 
in the reaction of a cell or a cell mass to some environmental differential, 
but after its establishment a gradient may persist through cell division or 
other reproductive process and so be inherited by the offspring of such 
reproduction. A gradient may be determined by the localization, 
experimentally or otherwise, of a region of increased physiological activity 
in a cell or cell mass. The gradient in its beginning may be nothing more 
than the gradation in activity from the center to the periphery of such a 
region. In consequence of growth the center of such a region may be- 
come an apical or anterior end of an axis. The environmental differen- 
tials which determine gradients may be of various sorts, light, electric 
current, local stimulation, differential exposure to oxygen, etc., and in the 
case of organ axes, buds, etc., the environmental factors determining the 
gradient may consist in the relations of the part concerned to other parts 
of the organism. 

"The high or most active end of a gradient may exercise a physio- 
logical dominance over other regions. This dominance in its more 
primitive form apparently decreases in effectiveness with increasing 
distance from the dominant region and if a part of the organism comes, 
either through increase in size of the organism or through decrease in 
dominance or certain other conditions, to lie beyond the range of dom- 
inance, physiological isolation of the part results and in many of the 
simpler organisms such physiological isolation may result in agamic 
reproduction. 

"The gradient theory has no quarrel with heredity. The gradient 
merely provides the plan, the pattern, the framework, so to speak, while 
the material and its possibilities are given in the hereditary constitution 
of the protoplasm in which the gradient exists." 



PLATYHELMINTHES 85 

Class (or Phylum) Nemertinea. (Gr. nemertes, true).— The 
Nemerteans are soft, contractile, chiefly marine flatworms some- 
times classed with the Turbellarian Platyhelminthes. They range 
in length from 5 mm. to 90 feet. 

The mouth is anterior and ventral and the anus is posterior. 
They have an eversible proboscis armed with stylets, indicating that 
it is functional both as a tactile and an ofl'ensive or food-t'aking 
organ. The digestive tract consists of an esophagus, stomach, 
intestine with paired diverticula or a long cecum, and a rectum. 
The circulatory system, not found in Platyhelminthes, consists of 
two or three longitudinal trunks with connecting branches. The 
blood sometimes contains hemoglobin. Excretion is effected 
through paired and many-branched longitudinal canals which open 
to the outside through pores. Most nemerteans are unisexual, 
and a few are hermaphroditic. The paired gonads discharge their 
products through the body wall, having no permanent genital ducts, 
A few are viviparous. Development is direct or in some forms by 
the metamorphosis of a free swimming larva, the pilidium (Desor's 
larva). (See p. 220.) The nervous system consists of a four-lobed 
brain with a pair of large lateral nerves uniting at the posterior end 
of the body, a dorsal median nerve, and, in some, a ventral median 
nerve. There are lateral ciliated cerebral canals related to the 
dorsal cerebral lobes. Certain species have as many as two hundred 
ocelli equipped with a lens and nerve, while others have two otolithic 
vesicles. 

Nemerteans are carnivorous, and feed on soft-bodied inverte- 
brates, certain large species capturing tubiculous worms. A few 
are parasitic, infesting Crustacea and mollusca, while others are 
commensals in the pharynx and atrial cavities of tunicates. 

References on Platyhelminthes 

Fantham, Stevens and Theobald's (1920) Translation of Braun's 

Thierischen Parasiten des Menschen. 
Linton, E. Many papers published by the U. S. Bureau of Fisheries. 
Stiles, C. W. Cestode Parasites of Man. Bulletins 25 and 28, U. S. 

Hygienic Laboratory. 
Stiles and Hassall. The Inspection of Meats for Animal Parasites. 

Bulletin 19, U. S. Dept. of Agriculture. 
Stunkard, H. W. Many papers listed in his bibliography, New York 

University. 



86 PLATYHELMINTHES 

Consult also papers listed in standard books on Parasitology, such as 
Castellani & Chalmers, Chandler, Rivas, Stitt, and Underhill. 

References on Nemertinea 

CoE, W. R. Synopsis of the Nemerteans, pt. i. Am. Nat., vol. 39, p. 

425. 
Verrill, a. E. 1892. Marine Nemerteans of New England and 

adjacent waters. Trans. Conn. Acad, of Sc, vol. 8, p. 332, 



CHAPTER VI 

Nemathelminthes. Nemas 

The Nemathelminthes (Gr. nema, thread; helmins, an intestinal 
worm) or Nemas live in fresh and salt water, damp earth and moss, 
and among decaying substances; many are parasitic. They are 
often minute in size and some may remain viable when dried. They 
vary in size from o.oi to i meter or more in length. 

Classification. (Modified) 

Class Nematoda 

Fam. I. Ascaridae. 

1. Anguillulidae 

3. Strongylidae. 

4. Trichuridae. 

5. Filaridae. 

6. Trichinellidae. 

Characteristics 

I. Elongate worms, many parasitic. 

1. Body usually cylindroid and unsegmented. 

3. A nerve ring with associated ganglia. 

4. Single and paired excretory organs, and tubular gonads. 

Natural History 
Dr. N. A. Cobb states (Nematodes and their Relationships): 

"The number of species of nematodes must be enormously greater than 
is commonly supposed. It may be estimated that more than 80,000 
nematode species infest the 40,000 species of vertebrates. Insects, 
much infested, will add many thousands of other species. The mollusks, 
crustaceans and various groups of worms are also infested and investiga- 
tions continue from these species also to augment the number of known 
species of parasitic nematodes. 

" Numerous as the parasitic species are, it is certain that the nematodes 
living free in soil and in water far out-number them; they probably con- 

87 



88 NEMATHELMINTHES 

stitute one of the important mechanical as well as biological factors in soil 
and in the bottom of lakes and oceans. Estimates based on (Dr. Cobb's) 
investigations show that in the upper foot of an arable soil the numbers 
of nematodes run to thousands of millions per acre." 

Longevity. — When in encysted condition in grains or in the soil, 
nemas may live for years. Needham found in 1743 that nematodes 
in wheat ears would live for several months in a dried condition. 
Baker found that nematodes dried for twenty-eight years became 
active again when moistened. (Becquerel. Latent Life. Scientific 
Am. Supp., vol. 82.) 

Family i. Ascaridae. — In the nemas of this family the body is 
thick, and the mouth has tnree lips always bearing papillae and 
amphids. The males are smaller than the females and have a curved 
caudal end. Numerous species attack the vertebrates and many 
of the invertebrates, living as parasites in their intestines, but found 
in other organs or in the body cavity. In general they require no 
intermediate host. 

Type of the Group — Ascaris lumbricoides. — Jscaris lumbri- 
coides, the human " eelworm," is found in the human small intestine 
where resultant lesions may induce the symptoms of anemia.^ 
Profound respiratory affections such as pneumonia may be caused 
by ascarids lodged in the lungs. It has been estimated that from 
10 per cent to 40 per cent of Europeans are infested with A. lum- 
bricoides. 

The females contain as many as sixty million eggs. After 
fertilization the eggs pass out of the body of the host with the 
feces. The eggs become embryonated in the soil. Such ova remain 
viable for five or six years. They enter the digestive tract through 
water or contaminated food. Dirt eaters sometimes take them in 
and it is possible that they may also enter with unwashed vegetables. 

Ascaris lufnbricoides has been found in the dog, sheep and hog. 
It possibly occurs in the cat and the rat. The host relationship 
of pig and human ascarids has been tested by feeding eggs of the 
human ascaris to pigs. They induced respiratory disturbances but 
did not become established In the digestive tract of any of the pigs. 

^ Wells, Jour. Paras., vol. 17, pp. 167-182, June, I931, found that a single dog- 
hookworm, a strongyle, see p. 92, may withdraw .8 cc. of blood from the host in 24 
hours. The Ascaridae may be extremely injurious also. The number of nemas as yet 
known and studied is relatively so small that their classification is still provisional. 



NEMATHELMINTHES 



89 



.^\ 



Excretory Pore 

Pharynx 



-Excretory Tube 



Oenito/ Pore 



— t/agino 



% 



^--Uterus 



-^4 — Ovary 



Eggs of the pig ascarls did not produce mature ascarids in the mon- 
key and the two human subjects. No intermediate host is required 
for the development of Ascaris hwibricoides. 

Anatomy.— TVq female Ascaris lumbricoides is about six inches 
long. It has a slender body tapering 
at both ends. The body is grayish 
pink in color with lateral stripes. 

Digestive Syste?n. — The month has 
one dorsal and two sub-ventral lips. 
The dorsal lip bears two large papillae, 
each sub-ventral lip bears a small 
lateral papilla and a large sub-ventral 
papilla. The amphids are small pores 
slightly dorsal to the lateral papilla. 
Amphids are supposed to be gustatory. 
The long muscular esophagus leads into 
the intestine which runs throughout 
the body, ending with a slightly smaller 
rectum that opens at the anus. Ab- 
sorption takes place through the walls 
of the intestine. 

Excretory System. — The excretory 
system consists of two longitudinal 
canals, one in each lateral chord; they 
open to the exterior through a single 
ventral pore near the post-pharyngeal 
region. (Figure '^i^d) 

Reproductive System. — The female 
reproductive system consists of two 
slender coiled, thread-like ovaries, con- 
tinuing into the dilated uteri which join 
to form a short tube, the vagina. The 
sperm from the male fertilizes the eggs 
in the uteri and the eggs pass out 
through the genital pore, situated about 
one-third the distance from the head, 
a shell resisting digestive juices. The male (about 4 inches long) 
has a sinale thread-like testis from which the vas deferens leads 
to the seminal vesicle and thence to the ejaculatory duct which 
opens at the rectum. 



--Intestine 



-Excretory Tub^ 



Fig. 36. Anatomy of a female 
round worm Ascaris. (After 
Shipley and McBride. Courtesy 
of Macmillan and Co., Ltd.) 

The eggs are covered with 



90 



NEMATHELMINTHES 



Nervous System. — A nerve ring encircles the esophagus con- 
nected to two large nerve cords, one ventral and one dorsal; with 
several other lesser cords and numerous nerve strands and connec- 
tives.^ 

Other Ascarids. — Parascaris equorum, the largest species of 
Ascaridae, is found in the horse family where it infests the small 
intestine. Males are eight to ten inches and females ten to twelve 
inches long. This species was used by Van Beneden in his classical 
study of chromosomes. It is said that one-third of the dry sub- 
stance of A. megalocephala consists of glycogen. 

Ascaris vitulorum infests calves, attacking the small intestine 
and sometimes ascending to the abomasum. It produces diarrhea, 
colic and intestinal inflammation. Ascaris ovis infests the small 
intestine of sheep. Ascaris suilla {lumbricoides) infests the hog's 
small intestine. If it enters the stomach it causes nausea; if it 
infests the pancreas it may occlude the bile ducts and cause jaundice. 
Infesting the lungs, it causes " thumps." Toxocara canis and 
Toxuscaris leonina infest dogs; Toxocara mystax infests cats. As- 
caridia lineata occurs in poultry, infesting the intestine. Ascaridia 
maculosa (syn. Heterakis maculosa) attacks pigeons. 

Enterobius (Oxyuris) vermicularis (Oxyuroidea), a white worm 
called the pinworm of man, is less than J/2 inch long. The male is 
2 mm. to 3 mm., the female 9 mm. to 10 mm. in length. The color 
is white, the body is expanded anteriorly. Metchnikoff believed 
the pinworm an important cause of appendicitis. Several con- 
flicting reports have since appeared, but there is good evidence that 
the eggs and larvae of the pinworm are found in diseased appendices. 
Oxyuris eqiii^ the horse pinworm, is found in the rectum and large 
intestine of the horse, ass and mule. 

Rhabditis nigrovenosa {Rhabdiasoidea). — In this form we find 
well marked the alternation of generations — hermaphroditic with 
sexual. It is found in the lungs of the frog and toad in a her- 
maphroditic condition. The eggs are laid and pass into the ali- 
mentary canal from the lung. They develop in water or soil into a 
nematode in which the sexes are separate. Fertilized eggs develop 
internally and eat all but the cuticle of the mother. From a free 
life in the mud they pass into the frog's lung, by way of its cuticle 
and mouth. 

1 For nervous system of Ascaris see Handbuch der Zoologie, v. 2, Achte Lieferung 
Teil (4) Bogen 23-32, ss. 280-283. 



NEMATHELMINTHES 91 

Family 2. Anguillulidae.— This immense group consists of 
small, thread-like nematodes which live in water, mud and soil, 
and also parasitically in plants and animals. 

Anguillula aceti, the vinegar eel,^ a frequent subject for laboratory- 
experimentation, lives in vinegar and stale paste. Tylenchus 
dipsaci {devastatrix) attacks oats, rye, clover, hyacinths, the ear 
cockle of wheat and about a hundred other plants. Tylenchus 
tritici attacks oats. Caconema {Heteroderd) radicicola attacks 
over seven hundred plant species, including tomatoes, cucum- 
bers, potatoes, turnips, peach trees, lettuce, and most other crops 
and weeds. In crop rotation it is most important to keep down the 
weeds. 

Lije History of Caconema radicicola.— The female is pear shaped, 
and about 1/25 of an inch or about one-half the diameter of the head 
of an ordinary pin. More than 500 eggs may be produced by one 
female. Some of these pass out to the exterior, but many remain in 
the body of the mother to develop, nourished by her remains and 
by egg yolk. Upon hatching, the larvae seek out roots of many 
species of hosts and drill into them by means of a protrusible oral 
spine. The irritation causes a swelling or tubercle, the root-gall or 
root-knot. The males pass through a larval stage and shed their 
skins, then travel through the root tissue, as long eelworms, pair 
with the females and die. Males are 1/12 to i/io of an inch long. 

Experiments showed that Heterodera schachtii, the beet-root 
nema, will travel thirty feet to a bed of germinating beet seeds. 

In warm climates, such as the southern states and parts of 
California, soil nematodes may pass through ten generations a year. 
In colder latitudes, freezing may destroy them. Their ability to 
encyst themselves preserves many in cases where the soil is porous 
enough to enable them to burrow deep and then encyst. Warm, 
moist sandy soils favor these nemas; heavy wet soils are less affected. 

Control. — The best method of removing plant parasitic nemas 
from the soil seems to be by rotation of crops. A few plants, like 
some varieties of wheat, millet, peanuts, rye, red-top, forw, cow-peas 
and soy beans, prove to be only slightly susceptible to Caconema 
{Heterodera) radicicola. In greenhouse soils, either stearn steriliza- 
tion or the use of hot water is effective. In the absence of weeds, 
lure-crops are used in greenhouses to advantage. 

1 Consult G. Zebrowski, 1931, "Anguillula Aceti— A Desirable Nema For Type 
Study." Science, vol. 74, pp. 390-391, Oct. 16, 1931. 



92 



NEMATHELMINTHES 



Family 3. Strongylidae. — This family is of especial interest to us 
since it includes the hookworm of man, the gapeworm of fowls, and 
many other internal parasites infesting domestic animals. While 
these parasites are ordinarily found in the digestive tract, strongylosis 
may be bronchial or pulmonic, intestinal, vascular or renal. Young 
animals suffer more than adults. Larvae of the hookworm cause 
profound irritation as they bore through the skin of the feet into 

lymph spaces. 

Dictophyme renale {Eustro7Jgylus visceralis) 
{S. gigas, Rud) is the largest of the Nema- 
thelminths. The females may reach a length 
of 39 inches. It infests the kidneys of Carni- 
vora (dog), Ungulata (horses, cattle) and 
even man. 

Strongyloidea {Dictyocaulus viviparus) 
{Strongylus tnicrurus) infests the bronchi and 
air cells of cattle and causes verminous bron- 
chitis. Dictyocaulus filaria infests sheep, 
goats and camels, attacking the bronchi and 
lungs. Metastrongylus elongatus attacks the 
bronchi and lungs of hogs. Strongylus elon- 
gatus paradoxus infests the fourth stomach 
(abomasum) of sheep, goats and cattle. 
Strongylus equinus bores through the gut into 
the blood vessels and causes aneurisms in the 
mesenteric vessels of the horse. Numerous 
other forms infest the domestic animals. A 
(After Jordan and Kel- very common parasite of the fowls is Syn- 
logg, Animal Life. ^^^^Z^J trachealis (Figure 37), the " gape- 
Courtesy of D. Appleton >> T L ^ • 1 r 
^ r- . worm. In the tropics several cases or 

human mrestation by gapeworms nave been 
reported this year (1931). 

Oesophagostoma radiatum forms cysts in the mucous membrane of 
the intestines of cattle. 0. columbianum, the nodular worm of sheep 
and cattle, produces nodules in the large intestine which have been 
mistaken for intestinal tuberculosis. 

Necator americanus., the hookworm of man (Figure 50, A., 5, C 
and D), causes tibial ulcer and dirt eating, besides weakness from 
loss of blood. The symptoms of hookworm include paleness, thin- 
ness, dull skin and eyes, dry hair, weakness, a depraved appetite for 




Fig. 37. Syngamus 
trachealis, the^ape-worm 



NEMATHELMINTHES 93 

ashes, tobacco, paper, plaster. Hookworm disease may be mistaken 
for anemia as the red corpuscles are deficient in number. The eggs 
pass out in the feces and if allowed to get into the soil will develop 
into tiny worms. Larvae of the hookworm enter the feet, boring 
through the skin into lymph spaces, thence via the lymph vessels 
to the veins and into the heart. The heart pumps them through 
the pulmonary arteries to the lungs. From the lungs (where they 
form lesions) they travel up the bronchi and trachea to the pharynx 
and are swallowed down the esophagus and into the stomach and 
intestine. They may come directly into the intestine from the mouth 
and esophagus, if taken in with dirty water or food. In the intestine 
they do not multiply, but the females continuously produce ova 
remaining there sometimes for three years. Nicoli showed (1917) 
that hookworm larvae will live in water for eighteen months, but 
Ackert found (1924) that at the end of that time, they were no longer 
infective.^ Ackert also discovered that larvae will live in water 
ranging from 45° to 98° F. The similar European hookworm {Ancy- 
lostoma duodenale), found first in English Egypt, is about 2/5 of an 
inch long, living in the small intestine of man. 

Ancylostoma braziliense., a worm infesting the small and rarely 
the large intestines of the cat, dog and fox, is the cause of " ground 
itch " in Southern United States. Reference has been made 
(page 88) to the important study of Wells (1931) on anemia pro- 
duced by the dog-hookworm. 

Through the activity of Dr. C. W. Stiles, U. S. P. H. S., and his 
co-workers in the Rockefeller Sanitary Commission,^ the hookworm 
is now being controlled in the United States and approaching 
control elsewhere. Dr. Stiles has pointed out (Scientific Monthly, 
October, 193 1, vol. 2>3^ PP- 362-364) that hookworm disease is even 
now one of the most important causes of backwardness in southern 
school-children. 

Family 4. Trichuridae. — These nematodes, placed under the 
family Trichinellidae by some writers, are called the " hair necks," 
as they have a long slender anterior portion which contains 
the esophagus. The head is nude and the mouth rounded. They 
are oviparous. 

2 Ackert, J. E. 1924. Studies on the longevity and infectivity of hookworm 
larvae. Am. Jour, of Hyg., vol. 4, no. 3, pp. 222-225. 

' Cort and his associates, in the International Health Board, have published more 
than thirty papers on hookworm disease, chiefly in the Am. Jour, of Hygiene. 



94 



NEMATHELMINTHES 



Trichuris trichiura {Trichocephalus trichiwis) lives in the large 
intestine near the cecum of man. It does not move and is sup- 
posed to be of little injury. The posterior part of the body is 
threadlike, while the anterior part is much narrower and hairlike. 
Related species infest the colon and cecum of sheep, cattle, dogs 
and hogs. 




embr 



B 




Fig. 38. A, Trichinella spiralis^ female. B, larvae in muscle, not yet encysted. 
C, encysted larva. (From Daugherty after Leuckart. Courtesy of W. B. Saunders 
Co.) 



NEMATHELMINTHES 95 

Family 5. Trichinellidae. (Figure 38, A, B and C.)— In the 
minute Trichinella spiralis, the body is thicker posteriorly and 
not so slender and filamentous anteriorly, as in the Trichuridae. 
The embryos develop in the uterus and are hatched there, so that 
the young are brought forth alive (viviparous). 

The Trichinellidae are found in the muscles of pigs, rats, mice, 
man, rabbits, guinea pigs, and dogs. They are not found in birds. 
Each larval worm is encysted in an oval capsule 0.4 to 0.6 mm. 
long. Cysts may number 100,000 to 125,000 per cubic inch of meat. 

Life History of Trichinella spiralis. — If the cysts are eaten, the 
digestive juices free the worms from the meat in which they are 
encysted. They then enter the small intestine and become mature 
in a few days. The female, 3 to 4 mm. long (male 1.5 mm.), 
penetrates the intestinal mucous membrane and in a month gives 
birth to 1,500-10,000 living young and then dies. Young are 
carried from the lymph vessels through the thoracic duct to the 
veins, and finally from the blood vessels they wander into the 
most actively used muscles of the body, such as the diaphragm, eye- 
muscles, and muscles of the neck. They destroy the sarcolemma 
and become encapsulated in cysts about 1.5 mm. long. High fever 
is a symptom of trichinosis. In Emmerslaben, Saxony, in 1884, 
there was an historic instance of one infected pig producing serious 
illness in 364 people, 57 of whom died in the space of one month. 

Within the past five years, a number of fatalities have been 
recorded, due to Trichinella infections, in these United States. 

Family 6. Filaridae. — These extremely minute elongated worms 
live in blood and lymph vessels, serous cavities of the body, and in 
subcutaneous connective tissue. The males usually have a spirally 
rolled tail, and the females have two ovaries. The majority of them 
are viviparous. None of the family are blood suckers. 

Filaria bancrojti, formerly called Filaria sanguinis hominis, 
is a slender, threadlike worm, the male about 40 mm. in length and 
the female about 100 mm. (4 inches). They live in the lymphatic 
glarids of man, and pass from the eggs into the blood and sometimes 
into the kidneys. They are supposed to cause elephantiasis by 
obstructing the flow of lymph. They are transmitted by night- 
flying mosquitoes. Loa loa, a smaller form, is transmitted by a 
biting fly ( Chrysops), which is day-flying. Filaria perstans is trans- 
mitted by a midge (Culicoides). It is essentially a parasite of the 
dark skinned races, rarely attacking the whites of West Africa. 



96 NEMATHELMINTHES 

Filaria equina infests the serous cavities and has been found in the 
aqueous humor and causes opaque cornea in the horse. 

The female Guinea worm {Dracunculus medinesis) is about thirty- 
six inches long and as large as packing twine. It produces abscesses 
under the skin in which the worm is coiled. Embryos must enter 
water and penetrate the microscopic crustacean Cyclops. The larva 
reaches man through drinking water containing Cyclops. Guinea 
worms occur in Asia, Africa, and tropical America. 

Mermithidae. — The hairworm, Mermis subnigrescens, is a 
parasite of the common grasshopper. The grasshoppers swallow 
the eggs with their plant food. The hairworm Agamermis decaudata 
also infests grasshoppers. Cobb and his associates have suggested 
that control of grasshoppers as pests may be aided by parasitizing 
them, thus causing sterility and death. They found that a high 
degree of parasitism caused all developing hairworms to become 
7nales and a low degree of parasitism resulted in the parasites all 
being females^ with a gradient (see page 84) between the extremes, 
corresponding to the degree of parasitism. The Mermithidae 
constitute a very large group, others of which infest injurious insects, 
such as mosquitoes, ants, cutworms, and the like. 

Forms Uncertain in Position Formerly Classed with the Nema- 
thelminthes — Acanthocephala. — In this group of " thorn-headed " 
worms, we find a protrusible rostrum or proboscis with five or more 
rows of recurved hooks. An alimentary canal is absent. An un- 
paired cerebral ganglion is present. 

The larva of Echinorhynchus gigas lives in the larva of the June 
bug (Melolontha). The adult worm is found in the pig, attached 
when full grown to the wall of the small intestine. It is dioecious, 
i.e., the sexes are separate. The ovaries of the female break up into 
free floating egg groups. The uterus picks up immature and fer- 
tilized eggs indiscriminately, but only the elongate, shelled ones may 
pass the canals; immature eggs are led by a ventral opening back to 
the coelom. In E. gigas, protonephridia open beside the genital 
opening. The oviducts of the female and the penis of the male are 
at the posterior end. 

Gordiaceae. — These minute, slender animals are commonly 
known as " horse-hair worms." They have an esophageal nerve 
ring, a ventral nerve cord and the female genital opening is at the 
cloaca. The larvae infest insects and the adults live in water, 
twining around plants and depositing their eggs. 



NEMATHELMINTHES 



97 



Treatment of Nematosis. — A diet rich in carbohydrates is 
said to lessen the damage to the liver, kidneys and adrenals that 
frequently ensues from the use of carbon tetrachloride in hookworm 
disease. Hexylresorcinol is also effective. (Science, Aug. 1 8, 193 1.) 

In certain pioneer studies, T. B. Johnson and W. W. Hodge, in 
May and June, 1913, determined the phenol coefficients of resorcinol. 



Vulva — 
Vat^tna 



Bipolar gang/ion cells-^- 
Nerve -rinq 
Lateral chord — ■■- 




Ovum in ejaculatory duct 



Ovary with c(^cjS In 

process of development 

Amphidiol nerve 



Excretory pore 

Coudol gland 



p^ £(^ in process of fertilization 

— Spermatozoa 

£<jq with shell 



Uterine wall 

C/vette 



Nucleus of 
Salivary glond 
£soptio^us- 

Cardia — 
Demonian system 



Rectum 



i' Renette duct 

— Renette CG/I 

^%@S?*^^^ Intestine 



— Spinneret 

Fig. 39. Marine free living Nematode, Metoncholaimiis pristiurus, female. Courtesy 
of N. A. Cobb. (Drawn by J. Danforth.) 



ethyl resorcinol and propyl resorcinol, three of the four points on the 
curve. A brief account of the work of Professor Hodge was pub- 
lished in 1913, Jour. Amer. Chem. Soc, vol. 2S-> P- ioi4> but it was 
not until 1921, Jour. Amer. Chem. Soc, vol. 43, pp. 348-360, that 
Hodge's curve with one more point added was published. 



98 NEMATHELMINTHES 

As an outgrowth of this pioneer work on alkyl-resorcinol deri- 
vatives, Doctor Leonard of Johns Hopkins University has developed 
the internal antiseptic "hexyl resorcinol." 

Thyynol in 6o-grain doses is effective in the treatment of human 
helminthiasis. The active principle of oil of chenopodium, called 
ascM-idole, is used in doses of 0.5 c.c. Calomel, santonin, and oil 
of male fern {Aspidiuni) are beneficial in trichinosis, but not effective 
after the parasites have become encysted. 

Nematodes as Laboratory Material. — Certain free-living aquatic 
nemas are so resistant to external conditions that they can be shipped 
alive long distances, and are thus favorable laboratory material for 
zoological courses in schools and colleges. Prominent among these 
are species inhabiting foul mud, such as Metoncholaimus pristiurus 
(marine) and its close relatives, and certain species of Dorylaimus 
(fresh water). M. pristiurus have been shipped thousands of miles 
both summer and winter, and used successfully.^ 

General Consideration of the Nemathelminthes 

Distribution. — Nematodes are found from the depths of the sea 
to the tops of mountains and in hot springs and Antarctic ice. 
While it was formerly supposed that they were almost all parasitic, 
it is now known that besides infesting animals and plants of all 
species, there are very many, small, free-living species. 

Physiology. — Nematodes usually have a simple digestive tract, 
well-developed excretory organs, tubular gonads and a nerve ring 
with sensory papillae and both dorsal and ventral nerves. 

Fossil Relatives. — The Nematodes range from the upper Paleo- 
zoic to the present. They are found in the Coal measures and 
parasitic in insects in the Tertiary amber. 

Ancestry and Relationships to Other Phyla. — The various classes 
of Nemathelminthes differ and it is still very doubtful whether they 
should be grouped into a single Phylum. Some of the families 
formerly classed under the Nemathelminthes are now separated, 
apparently resembling the Annelida. 

References on Nematodes 

Chandler, A. C. 1922. Animal Parasites and Human Diseases. J. 
Wiley and Sons, N. Y, 

* Cobb, N. A. 1 93 1. Science, vol. 74, pages 489-490. 



NEMATHELMINTHES 99 

Cobb, N. A. 1914. Nematodes and their Relationships. Year Book 
of U. S. D. A., 1914, and many papers. 

CoRT, W. W., AND Associates. (Many papers in Am. Jour, of Hy- 
giene.) 

Harris and Brown. 1925. Oxyuris vermicularis as a causative factor 
in appendicitis. Jour. Am. Med. Assoc, vol. 84, no. 9, pp. 650-654. 

Stiles, C. W. 1903. Hookworm Disease. Bulletin 10, Hygienic Lab., 
Washington. 

Stiles, C. W. 1910. Hookworm Disease. Pub. Health Bulletin 32, 

Washington. 
Stiles, C. W. 1910. Soil pollution as cause of ground itch, hookworm 

disease and dirt eating. Circ, Rockefeller Sanitary Commission 

for the Eradication of Hookworm Disease. 
Underhill, B. M. 1924. Parasites and Parasitosis of the Domestic 

Animals. Macmillan Co., N. Y. 
Ward, H. B., and Students. (See bibliography from Univ. of Illinois.) 



CHAPTER VII 

Annelida or Annulata 

The older terminology included the Molluscoidea, the Platyhel- 
minthes, the Trochelminthes, and the Nemathelminthes with the 
Annelida under the general term Vermes. For several decades, 
however, the Phyla have been separated. 

The Annelida (Lat. annellus, a little ring) are the most highly 
developed of the worms, with regularly segmented bodies, which in 
most cases indicate by external annulations the metameric arrange- 
ment within, which is such that the internal organs are repeated in 
each segment. The head usually has a " prostomium " in front of 
the mouth. (See Figure 45.) 

There is usually a well-developed coelom, and an extensive 
series of blood vessels. Hair-like or comb-like gills function in 
respiration in some forms, while in others minute capillaries in the 
skin aerate the blood. The excretory organs, called nephridia, are 
segmentally arranged and the nervous system consists of dorsal 
cerebral ganglia, and a ventral nerve cord with segmentally arranged 
ganglia. 

Classification 

I. Class Archi- Annelid a (Gr. arche, beginning; Lat. anne//us, a little 

ring) without setae or parapodia. 
1. Class Chaetopoda (Gr. chaite, bristles; pons, foot) with setae. 
3. Class Hirudinea (Lat. hirude, a leech) without setae or parapodia, 

but with suckers. 

Characteristics 

1. Segmented worms in which the segmentation is in most cases 

visible externally. 

2. Appendages paired, not jointed. 

3. Setae are present in the body wall. 

4. The coelom usually communicates with the exterior by paired 

nephridia, and pores. 

100 



ANNELIDA OR ANNULATA loi 

5. The nervous system consists of two dorsal ganglia, connecting 

commissures passing around the pharynx, and a ventral 
chain of ganglia with lateral nerves. 

6. The alimentary canal is well developed and usually specialized. 

7. Trochophore larva found in many forms. 

Natural History 

Class I. Archi-Annelida. — The most primitive of the Annelida 
are the Archi-Annelida, represented by two families, both marine 
and exceedingly small. The family Folygordiidae includes the 
sand-living form Polygordiiis. It is slightly over an inch long, with 
indistinct external annulations, but a septate coelom, and metameric 
development of nephridia, gonads, digestive tube and ventral nerve 
cord. The larva has a trochophore stage. 

The family Hist7~iodrilidae are minute parasitic worms infesting 
the lobster. They have three horny jaws, a well-developed digestive 
system consisting of esophagus, intestine and rectum; and have 
primitive united cerebral ganglia. The sexes are separate. 

Class 2. Chaetopoda. — In the Chaetopoda, segmentation is 
distinct both internally and externally, and the setae are segmentally 
arranged on the parapodia or sunk in pits. 

Order 1. Polychaeta. — The polychaetes are chiefly marine 
animals, with setae arranged in groups on the fleshy parapodia. 
They have a distinct head, usually provided with sense organs. 
The prostomiufn bears from one to ten dorsal tentacles and two ventral 
palps, which in certain forms are broken up into long respiratory 
filaments. The sexes are usually separate. Eyes are present on 
the prostomium of some forms, and lithocysts in a few forms (^reni- 
cola). Polychaetes are of diflferent colors, including red, blue, green, 
or yellow. They usually pass through a trochophore stage. (See p. 
125.) 

Heterogony is present in Nereis, a small pelagic form alternating 
with a large bottom living one. The palolo worms of Samoa 
{Leodice viridis) come to the surface during the October full moon to 
breed and are caught by the natives who use them for food. 

A few polychaetes are found in fresh water; the rest are marine, 
and chiefly bottom living animals, which burrow in the sand or live 
in tubes. The free-living forms are predaceous; the sedentary ones 
Hve on all kinds of organic matter. There are many commensals 
and a few parasites. (See p. 483.) 



I02 



ANNELIDA OR ANNULATA 



SyUidae are brightly colored forms less than an inch long, which 
are frequently found associated with sponges; some have an al- 
ternation of generations, in Autolytus for example (Fig. 40) an 
asexual individual sending off from its posterior end buds which 
become male or female. 

Aphroditidae are scale bearers, the scales, called elytra^ acting 
as breathing organs. Lepidonotus squamatus has twelve pairs of 
elytra. Polynoe, a small form about an inch 
long, has a large proboscis, with four strong jaws 
and a circle of papillae. It has twelve pairs of 
scales. Aphrodite, sometimes called the " sea 
mouse," is about five inches long and of a bril- 
liant iridescent color. 

Phyllodocidae are green and usually iridescent, 
with a long head which bears four pairs of short 
and four pairs of long tentacles. They secrete 
slime which binds mud together. 

Nereidae include the common Nereis, which 
may reach a length of eighteen inches. The 
" clam worm," as it is called by fishermen, is 
bluish green in color, and lives during the day in 
burrows in the sand, but comes out during the 
night, and is preyed upon by fishes. 

Nephthydidae are dorsi-ventrally flattened, 
elongate worms, whitish in color with a distinct 
red dorsal blood vessel. They are found in sand 
and mud along the shore. 

Leodicidae {Eunicidae) include the Pacific 
(Samoan) palolo worm, and the Atlantic palolo 
worm {Leodice fucatd) of the West Indies and 
the Gulf of Mexico, which swarm within three 
days of the full of the July moon. (See the Sa- 
moan palolo, page 118.) Diopatra is a large reddish brown worm, 
found from Massachusetts to South Carolina, in long tubes which 
project above the surface. Diopatra reaches a length of twelve 
inches, but is difficult to capture on account of the speed with 
which it hides in its tube. (Fig. 41.) 

Glyceridae include forms which are smooth, about eight inches 
long, and have many segments. The small conical head has many 
tentacles. The long proboscis has four hooked jaws. The Seden- 




FiG. 40. A sex- 
ual individual of 
Autolytus with 
male about to de- 
tach. (From Ver- 
r i 11 , Invertebrate 
Animals of Vine- 
yard Sound.) 



ANNELIDA OR ANNULATA 



103 



Moufh 



—Peristomlal cirrus 



taria lack both jaws and a protrusible pharynx. They have small 

uncini, or hooked setae, and a few hair setae. Some species form 

calcareous tubes (Serpula), while others use the material available, 

furnishing a cement by which they bind together sand, shells, or 

sea weed into protective 

coverings. The Spion- 

idae include a number 

of small burrowing 

worms with long peris- 

tomial cirri curving over 

the back, and with the 

dorsal cirri serving as 

gills. The proboscis 

lacks jaws. The Chae- 

topteridae include fifteen 

species of short, stout 

worms, which live in 

parchment-like tubes. 



Wino , a porapodium 





Fig. 41. Diopatra cuprea. 
(From Verrill.) 



Fig. 42. Chaetopterus pergamentaceus. (Original 
drawing by H. Lammers.) 



Certain species are highly phosphorescent. Important studies in 
Experimental Embryology have been made with the Woods Hole 
species, C. pergaynentaceus. (Fig. 42.) In the Tej'ebellidae we find 
a cylindrical body, having many similar lobes, and with well-de- 



I04 



ANNELIDA OR ANNULATA 



veloped mucus-forming glands. Amphitrite (Fig. 43) reaches a 
length of fifteen inches, and is reddish brown in color. It is found 
in sand and mud at low water mark. Polycirrus (the blood worm) 
is a long, slender, blood-red worm which does not form a tube, and 
has no branching gills. The Amphictenidae are small worms which 
form portable tubes of sand open at both ends. Cistenides {Pec- 
tinarid) gouldii is a flesh-colored form found in shallow water from 

North Carolina northward. 
The Cirratididae are worms 
with a cylindrical body, having 
many similar segments with 
long filamentous cirri. They 
live in burrows. 

Maldanidae form sand 
tubes. They lack gills. Cly- 
menella is one of the commonest 
types. The Arenicolidae are 
represented by but two com- 
mon species. Arenicola mar- 
ina^ called the " lug-worm," 
reaches a length of ten inches. 
It has twelve pairs of branched 
red gills on the central seg- 
ments. It burrows as much as 
two feet into the sand, but can 
be located by castings at the 
entrance. The Sabellidae in- 
clude a number of genera. 
The tentacles are rudimentary, 
the palps very large. A proboscis is present. They form mem- 
branous tubes in mud and sand. Example — Sabella jnicrophthalma. 
Serpulidae form long contorted calcareous tubes which are found 
incrusting shells. {Serpula or Hydroides^ 

Older 2. Oligochaeta. — These hermaphroditic annelids lack 
tentacles and parapodia, and have only a few setae, projecting from 
pits in the body wall. Certain oligochaetes have external gills 
{Nais). The head is not distinct, but has a small projection, the 
prostomiujn, and ^ peristomiuniy which contains the mouth, but lacks 
setae. Paired ovaries and testes are present in each animal, and 
seminal receptacles store the sperm prior to the extrusion of eggs 




Fic. 43. 



Tufted worm {Amphitrite ornatd). 
(Drawn by V^errill.) 



ANNELIDA OR ANNULATA 



105 



and sperm into a cocoon, which is secreted by the modified clitellum. 
There is no metamorphosis. The oligochaetes are singularly lacking 
in sense organs, pigment eyes being found in the Naids. We shall 
mention only five of the eleven families. (Figure 44.) 

Aelosomatidae are microscopic fresh water worms, whose red, 
yellow and brown oil globules make them appear spotted. They 
reproduce by fission, and 
are considered the most 
primitive oligochaetes. 

Enchytraeidae are slender 
small worms found in plants 
and in fresh water, near the 
sea shore. Their blood may 
be colorless, red or yellowo 
The small white form, 
Enchytraeus albidus^ is re- 
commended by Gamble as 
exceedingly useful for obser- 
vation under a binocular 
microscope. It requires a 
temperature not higher than 
60° F. 

Naidae are small, trans- 
parent, aquatic forms with 
a distinct head, and from 

two to four groups of setae on each segment. In Nais^ a common 
fresh water species, the blood is yellow or red. Eyes are usually 
present. Budding is a common form of reproduction. The Tubifi- 
cidae are slender reddish worms living in tubes, from which they 
protrude the posterior end into the water. Many species of Tubifex 
are found in brackish water; a few occupy fresh. 

Lumbricidae include the common earthworms. Among them 
are the familiar Lu7nbricus terrestris of Europe and America; 
Eisenia {Allolobophora) foetida, commonly found in manure; and 
Helodrilus^ represented in America by ten species. Aristotle called 
the earthworms the " intestines of the earth." 

Order 2. Oligochaeta. Fam. Lumbricidae. Type — Lumbricus 
terrestris. — The earthworm is from 5 to 18 inches long, with 100 to 
160 segments, strongly marked by external rings. A tropical 
species, Alegascolex australis^ reaches a length of eleven feet. 




Fig. 44. Nats. (From Leunis. Davenport's 
Zoology. Courtesy of The Macmillan Co.) 



io6 



ANNELIDA OR ANNULATA 



Anatomy. — At Its anterior end, Lumbricus terrestris has a pro- 
boscis-like fleshy lobe called the p7'Ostomium, with a mouth imme- 
diately behind it on the ventral side. The skin is covered by a 
transparent cuticle which is slightly iridescent, and is externally 
marked by annulations representing true segments. All segments 
except the first and the last have four pairs of setae, two pairs being 
ventral and two pairs ventro-lateral. (Fig. 45, A and B.) 

From the 31st to the 37th somite, the clitellum is situated. This 
aids the worms in adhering at mating and furnishes a slimy sub- 



~ ~ — Prostomium 



-A Mouth 




Seta 




A 



B 



Fig. 45. A, ventral view of the first four segments of Lumbricus terrestris, showing 
rows of setae. B, enlarged seta. (Drawn by W. J. Moore.) 



Stance that hardens into the cocoons In which the eggs are fertilized 
and develop. The setae of the 26th somite are modified for repro- 
duction. 

The external openings Include the mouth and anus at opposite 
ends. There are two nephridiopores for each somite except the first 
three and the last. The two pairs o{ seminal receptacle openings are 
found between the ninth and tenth and the tenth and eleventh 
somites. The two oviducal openings are at the 14th somite. The 
two vasa deferentia at the 15th somite are readily seen. There are 
also dorsal pores on the middle line of the back between the rings, 



ANNELIDA OR ANNULATA 107 

from the 8th somite to the last one, which permit the passage of 
fluids from the coelom to the skin. The anus is at the posterior end. 

Skin. — The thin protecting cuticle is formed from the living cells 
of the hypodermis beneath. The hypodermis consists of a single 
layer of cells most of which are covering and supporting, but some 
of which are modified into glandular (mucus) cells, and others into 
nervous cells. The nerve cells are connected with sensory fibers 
passing into the nerve cord, and the animal is very sensitive to 
light, touch and chemically different substances. The setae which 
are chitinous are worn away and replaced by reserve setae that 
grow from the main seta-sac. 

Muscular System. — The circular muscles lie immediately beneath 
the hypodermis and, contracting, elongate the segments. The 
longitudinal muscles, contracting, draw the ends of the segments 
towards each other, and the direction of the setae determines whether 
the movement is forwards or backwards. 

Body Cavity. — The body cavity, lined by peritoneum, contains 
the digestive tract, gonads, nephridia, circulatory system and nerv- 
ous system beside the coelomic fluid with yellow cells, derived 
from the walls of the intestine, and the phagocytic amebocytes which, 
like the phagocytic white corpuscles of man, engulf poisonous 
particles. 

Digestive System. — The mouth or buccal cavity (1-3 somites) 
leads into the pharynx (4-5 somites), with glands which moisten, 
and with powerful muscles which force food on. External muscles 
attached to the body wall expand the pharynx. The esophagus 
(6-i4th somite) has three pairs of saccular calciferous glands, at the 
loth, nth, and 12th somites, secreting calcium carbonate, which 
neutralizes the free acid of the soil. The secretions from the 
posterior pairs of calciferous glands open into the anterior pair, and 
thence into the esophagus. (Figure 46.) 

The three pairs of glands are really parts of one glandular struc- 
ture, which extends from somites 10 to 14. In many specimens of 
Lumbricus terrestris, the only distinct enlargements are in somite 10. 
The crop (15th and i6th somites) is for storage, and mixture with 
the secretions of the calciferous glands. The gizzard (17th and i8th 
somites) grinds the food with sand and gravel. The stomach- 
intestine (19th somite to anus) has a median dorsal infolding, the 
typhlosole, that increases the surface for absorption and retards the 
passage of food. 



io8 



ANNELIDA OR ANNULATA 




Prostomium 



Cerebral ganglia ('brain) 

—F'/lorynx 
-Pharyngeal muscles 

—Seqmen t 
— Septum 

—A Nephr.idium (enlarged) 

Serninal vesicle I 

-Aortic arch (dorsal heart) 

-Seminal receptacles 

Seminal vesicle Z. 

Calciferous gland 

— E:sophQ<^us 

Seminal vesicle 3 



Crop 

Giz:zard 

-Dorso-infesfinal blood vessels 
■Dorsal blood vessel 

Stomach- infest in e 
■Lateral diverticulum 



Fig. 46. Internal anatomy of the earthworm. (Drawn by W. J. Moore and Norris 

Jones.) 



ANNELIDA OR ANNULATA 109 

The stomach-intestine has secretory cells that furnish a digestive 
jfluid corresponding essentially to the pancreatic juice of the mam- 
mals, as it digests proteins, carbohydrates and fats. Albumin is 
broken down in y/2 hours at 37° C. in an alkaline medium, or 28>^ 
hours in an acid medium. It is believed thac a peptolytic ferment 
is present that accounts for slow digestion in an acid medium. An 
amylotic ferment diastase changes starch into sugar (maltose). An 
emulsifying ferment acts on the fats. Absorption is by osmosis and 
the blood transports the nutriment. The rectU7n is the posterior 
part of the intestine and has no typhlosole. It opens to the outside 
through the posterior anus. 

Circulatory System. — There are 5 longitudinal blood vessels; 
I dorsal, i ventral, i subneural and 2 lateral neural vessels; 5 pairs 
of doj-sal hearts or aortic arches (7-1 1 somites). Parietal vessels 
connect the dorsal longitudinal vessel to the subneural. 

In the first 12 somites the dorsal vessel is not a collecting vessel, 
but behind the last pair of hearts in the nth somite, it receives 
blood from the body wall and the alimentary tract. Two longi- 
tudinal trunks lateral to the alimentary canal collect blood from the 
anterior somites and passing posteriorly, join the dorsal vessel in 
the 1 2th somite. 

From the posterior part of the body the blood is carried forward 
in the dorsal vessel as far as the " hearts " which force it into the 
ventral vessel. Valves in the aortic arches and dorsal blood vessel 
prevent the blood from returning. The ventral vessel distributes the 
blood, which flows anteriorly in front of the aortic arches and 
posteriorly through the remainder of the body wall, nephridia, and 
alimentary system. Aerated blood returns to the dorsal trunk 
through the subneural and intestinal vessels. 

There are two distinct fluids which remain separated. The 
coelomic fluid is found between the gut and the body wall. The 
haemolymph is found in a series of closed tubes. The coelomic 
fluid corresponds to the lymph of higher animals which bathes the 
individual cells of the body. Haemolymph is apparently a solution 
of haemoglobin. The red fluid corresponds to red blood corpuscles 
of the blood of the higher animals and serves as a carrier of oxygen 
to various cells and tissues of the body. 

In marine worms the respiratory pigment is called chloro- 
cruorine. It is ^or^^jyr/w combined with iron. Some marine forms 
like Arenicola and Nereis have brilliant red blood; Aphrodite and 



no 



ANNELIDA OR ANNULATA 




I 



ANNELIDA OR ANNULATA m 

Polynoe have pale yellow blood; but in Sabella It is an olive green. 

The nervous system is well supplied with blood, having two 
lateral neural and one subneural vessel for the nerve cord. At room 
temperature (i2°-i8° C.) in Lumbricus terrestris, the dorsal vessel 
pulsates about fifteen to twenty times per minute, and in Nereis 
(marine sand-worm) it is about eight times per minute. Respiration 
is osmotic. There are many capillaries under the cuticle. 

Excretion. — Paired nephridia are found in each segment except 
the first three and the last. The receiving opening, the ciliated 
nephrostome, is situated one segment anterior to the one contain- 
ing its own yuphridium and nephridiopore. From the nephrostome 
or funnel, currents flow into the ciliated neck which passes through 
the anterior wall of the segment behind, then into a narrow tube 
which coils three times and then opens into a wide glandular tube^ 
which expels the waste at the external opening, the nephridiopore. 
About half of the nephridiopores are situated on the ventral surface 
in front and slightly laterad to the outer seta of the inner double 
row; while the remainder of the excretory apertures are high up on 
the side of the animal, dorsad to the row of dorsal seta bundles, at 
irregular distances.^ 

Solid wastes pass out the anus and gaseous wastes through the 
dorsal pores of the body wall, which are mid-dorsal, in the groove 
between the segments. The first one is between segments ten and 
eleven and opens into segment eleven. 

Reproductive System. (Figure 46.)— The earthworm is hermaph- 
roditic (monoecious) with the gonads of both sexes, but does not 
fertilize its own eggs. 

Female 

Internal Structures External Structures 

Ovaries, 13th somite. Oviducts opening at 14th somite. 

Two pairs of setninal receptacles. Openings to the seminal receptacles be- 

tween the 9th and loth; and the 
loth and nth somites. 

^ In our description of the earthworm it will be noted that certain errors of most 
textbooks have been corrected, particuhirly in treating of the calciferous glands, the 
position of the nephridiopores, and the collecting vessels in the anterior somites. Such 
corrections were inspired by the paper by Frank Smith, Certain differences between 
text book earthworms and real earthworms. Trans. 111. Acad. Sc, vol. 17, pp. 78-83. 
For systematic study of the Annelida, see Verrill, A. E., 1880, New England Annelida. 
Trans. Conn. Acad. Sci., vol. 4. 



112 



ANNELIDA OR ANNULATA 



Male 

Paired testes in the loth and nth so- 
mites. 

Three pairs of seminal vesicles at- Paired vasa deferentia opening at the 
tached from the 9th to the 12th 15th somite, 
somite. The last pair, bi-lobed, 
extend down over the 13th and 
sometimes the 14th somite. 





CO 


crc 




! F- 




\ PJl 

MR 

Fig. 48. Nervous system of the earthworm. Drawing showing a lateral view 
of the arrangement of the larger nerve trunks in the left half of the anterior segments 
of the earthworm, Lumbricus terrestris. A, nerve from lateral region of cerebral 
ganglion which passes to prostomium; AN, dorsal ramus of anterior segmental nerve; 
AR, ventral ramus of anterior segmental nerve; 5, nerve from near middle region of 
circumpharyngeal connective which passes to segment i; 5C, buccal cavity; C, nerves 
from ventral region of circumpharyngeal connective which pass to segment 2; CG, 
cerebral ganglion; CPC, circumpharyngeal connective; D, branch of nerve to pro- 
stomium that supplies tissues of dorsal region of buccal cavity; £, nerve that supplies 
the portion of the prostomium in the dorsomedian region of segment i; F, gangliated 
thickening of enteric nerve plexus; G, branch of nerve to segment i that supplies 
tissues of ventral region of buccal cavity; L, septal nerve; M, mouth opening; MTV, 
dorsal ramus of median segmental nerve; MR, ventral ramus of median segmental 
nerve; P, prostomium; PN, dorsal ramus of posterior segmental nerve; PR, ventral 
ramus of posterior segmental nerve; SG, subpharyngeal ganglion; I-VI, segments i to 6. 
(Courtesy of W. N. Hess, Journal oj Experimental Zoology, vol. 40, p. 235.) 

Conjugation. — Two earthworms pair so that segments 9, 10 and 
II of each animal are opposite the clitellum at segments 31-37, and 
the vasa deferentia of each animal are nearly opposite the 26th seg- 
ment of the other where the setigerous glands are modified. Mucus 
secreted by the clitellar and other glands of each worm becomes 
hardened into a single " slime-tube " encasing both animals from the 



ANNELIDA OR ANNULATA 



"3 



8th to the 37th somite. Two parallel 
lines extend posteriorly from the vasa defe- 
rentia to the clitellum, forming primitive 
channels for the passage of seminal fluid. 
Within the slime-tube the seminal fluid 
flows, containing free spermatozoa and 
spermatophores. The spermatophores 
are deposited in the seminal receptacles of 
the other worm and the slime-tube is 
soon left. 

Fertilization. — Later on at the appear- 
ance of the capsule or cocoon, formed by 
capsulogenous glands in the clitellar 
region, the 4-6 mature eggs are picked up 
at the egg-sacs opening at the oviducal 
apertures in the 14th somite; and the 
sperms that were stored in the receptacles 
are secured at their openings between the 
9th and loth and the loth and nth 
somites. Fertilization is effected in the 
cocoon at the time it slips off over the 
head, and since the sperms are from an- 
other animal, self-fertilization is pre- 
vented. In Lumbricus comtnmiis, two 
embryos are produced as a rule, in many 
cases arising as twins from a single ovum. 
Foot found (1898) that the total number 
of eggs in 100 cocoons was 399, about 4 
to a cocoon. Isolated worms deposit 
cocoons for weeks. 

The observations of Foot and Wilson 
have been to some extent contradicted by 
Grove and Cowley (1926), who found in 
Eisenia foetida that cocoon formation 
does not take place while the worms are 
still united by the conjugation slime tube.^ 

2 Grove, A. J., and Cowley, L. F. 1926. On 
the reproductive processes of the brandling worm, 
Eisenia foetida (Sav.). Quart. Jour. Microsc. Sci., 
70 (4), 559-581- 



KL A> 



Fig. 49. Sperm transfer 
in Lumbricus terrestris, 
(Drawn by W. J. Moore.) 



114 



ANNELIDA OR ANNULATA 




ANNELIDA OR ANNULATA 115 

They noted that after conjugation, a new slime tube is formed 
extending from the 7th to the 34th segment and that the eggs pass 
back into the cocoon, before it leaves the region of formation at the 
clitellum. Whether the sperms are squeezed out as the capsule 
reaches the apertures of the seminal receptacles, or they are also 
passed back to the capsule, the authors are not certain. 

Nervous System. — In the worms we have well-developed cerebral 
and ventral ganglia, constituting the centralization stage in the 
evolution of the nervous system of invertebrates. A bilobed brain 
(paired cerebral ganglia) sends off two circumpharyngeal connectives, 
which unite at the subpharyngeal ganglion. A ventral nerve cord 
has a ganglion in each segment, with three pairs of lateral nerves. 
Two pairs come off at the ganglia and one pair between the ganglia. 
Afferent nerve fibers are sensory; efferent nerves are motor. Stough 
(Jour. Comp. Neurol., vol. 40, no. 3, June, 1926) has shown that the 
giant fibers, seen in cross sections of the earthworm nerve-cord, are 
strictly segmental structures, and consist of a large number of 
closely applied parallel axones. Epidermal sense organs, chiefly lo- 
cated anteriorly and posteriorly, were discovered by Fanny Lang- 
don when a college Junior. (Figure 50.) 

Behavior. — Earthworms react to the ordinary stimuli of light, 
temperature, chemicals and electricity. They are very susceptible 
to the contact stimuli produced by vibrations. It is reputed that 
one way to drive earthworms from their burrows is to bore with a 
sharp stake into adjacent soil. 

Several articles have appeared recently regarding the so-called 
" singing " of earthworms. Apparently reliable reports have been 
made of the peculiar noises, possibly due to the rasping of the setae 
over stones or pebbles. Clark (Animals of Land and Sea) states 
that the singing girls of Java sometimes swallow earthworms in 
the hope that the tinkling sound will be " imparted to their voices." 

Class 3. Hirudinea — Leeches. — Hirudo medicinalis, the medic- 
inal leech, has a deep olive hue, is velvety, two to three inches in 
length, hermaphroditic and is found in Europe, America, Turkey 
and Africa. Medicinal leeches live 15-20 years, and are adult at 
5 years. They inhabit water; the female deposits 15-20 eggs in a 
cocoon. These hatch in 3-4 weeks. 

External Anatomy. — Their external segmentation does not cor- 
respond to the internal. There are usually 5 external grooves to 
each segment. The medicinal leech has 2 suckers. 



ii6 ANNELIDA OR ANNUL AT A 

Digestive System. — The digestive tract consists of the mouth, 
with three jaws, armed with chitinous teeth, a pharynx, esophagus, 
crop with eleven lateral diverticula, stomach and an anus. A 
secretion called deutero-albumose (hirudin) prevents the blood from 
clotting. It is formed by the glands located near the jaws. The 
muscular pharynx dilates to receive the blood and passes it on 
through the short esophagus to the crop which has 1 1 pairs of lateral 
diverticula and which stores the blood until it is digested in the 
globular stomach. No digestion takes place in the lateral " pockets." 
The rectum., situated between the last two diverticula^ is separated 
by a sphincter muscle from the true stomach. It ends as the dorsal 
anus near the posterior sucker. 

Circulatory System. — There are two main lateral vessels running 
longitudinally. These are connected with each other by looped 
vessels which give off many branches. There are two sinuses., one 
dorsal and one ventral, with numerous primitive lymphatic vessels. 
The blood is red with many white blood corpuscles. The leech has 
a body temperature of about 57° F., except when it has just gorged 
with mammalian blood. 

Respiration is carried on by the highly vascular skin. Experi- 
ments have shown that leeches will live in pure Nitrogen for from 2 
to 6 days. 

Excretory System. — Seventeen pairs of nephridia, from the second 
to the eighteenth segment, open laterally on the ventral surface. 
There are about five external annulations to each true segment. 

Reproductive System. — Leeches are hermaphroditic. There are 
nine pairs of diffuse testes^ which are situated on each side of the 
nerve cord. The spermatozoa pass by a short canal into the long 
wavy vasa deferentia. From these they travel in the epididymis 
where they are bundled into spermatophores and pass out by the 
penis. They leave the body in the mid-ventral line between rings 
30 and 31. 

Two small tubular ovaries are enclosed in vesicles., continuing into 
oviducts which unite as a uterus. Glandular cells secrete into the 
uterus a mucus fluid which later hardens into a cocoon. 

The genital pore is situated in the mid-ventral line at rings '^^ 
and "^^^d (segment 11). Conjugation consists in the actual simul- 
taneous insemination of each worm by the other. Spermatophores 
may remain for a long time in the uterus or may travel almost 
immediately in the female ducts and fertilize the eggs at the ovaries. 
Cocoon formation results. 



ANNELIDA OR ANNULATA 117 

The Nervous System consists of a pair of dorsal ganglia situated 
above the pharynx and of a double commissural nerve cord with 23 
ganglia. The dorsal, supra-esophageal ganglia are connected with 
the sub-esophageal pair by a rather narrow nerve ring surrounding 
the esophagus. The sub-esophageal ganglia represent five pairs of 
fused ganglia. From the dorsal ganglia, nerves supply the " eyes " 
and tactile and gustatory organs. The last ganglion gives rise to 
seven pairs of nerves. The h-ain gives rise to five pairs of optic 
nerves. There are ten " eyes " and many olfacto-gustatory and 
tactile sense organs. 

Allied Injurious Leeches.— Hirudo sanguisaga is found in the 
nasal passages of man. Haemopis vorax, the horse leech, is taken 
into the mouth when young by horses and cattle. It lives in ponds, 
ditches and springs and attacks man, the horse, ox, camel, and dog. 
It may become attached to the mouth, pharynx or even descend to 
the trachea. It is also found attached to the conjunctiva. It 
produces anemia, emaciation and even death. The treatment is 
strong salt solution, alum, and tar. The tar causes coughing and 
expulsion of the parasites loosened by the action of the salt and 
alum. If the water is stocked with fish or filtered through sand, 
the parasites are destroyed. 

The land leeches^ Haemadipsa Zeylanica^ are wiry, active forms, 
thin as a knitting needle, i inch long and not more than }4 inch in 
diameter. They attach to the legs of man and animals. They are 
found in Ceylon, India, the East Indies, Japan, Australia and South 
America. 

Adaptation of the Leech to Its Mode of Life. — The leech is re- 
markably adapted to its habitat. It can swim with great rapidity; 
it is protected by a rather tough hide. It has a mouth with 3 jaws 
armed with chitinous teeth, a crop with 1 1 lateral diverticula capable 
of storing enough blood to last 9 months. It takes in 3 times its 
own weight at one time. Not only does it have anterior and poste- 
rior suckers, but it secretes a substance " hirudin " said to be 
deutero-albumose, which prevents blood from clotting. 

General Considerations 

Distribution. — The Chaetopoda, which include earthworms and 
aquatic worms found in both salt and fresh water, are distributed 
widely. Very few are parasitic but a number are commensals. It 



ii8 ANNELIDA OR ANNULATA 

is estimated that the average field soil has 150,000 earthworms to 
the acre. 

Some fresh water Oligochaeta form tubes of mud held together by 
a mucus secretion. Others like the marine Chaetopterus form a 
yellow, parchment-like tube. Some species like Hydroides (^Serpidd) 
form lime tubes on shells. Sabellaria, an aberrant form, builds 
reefs on porous rocks from sandy tubes. Some species excavate 
galleries in rock or corals. 

Behavior. — The palolo-worm^ Eunice, found in the Pacific coral 
reefs, swarms during the last quarter of the moon in October and 
November. The sexual posterior part of the worm (called the 
epitoke) separates from the sexless anterior portion {atoke) and floats 
on the sea, giving off spermatozoa and eggs. Fishermen prepare 
their nets and boats and capture these worms in great numbers, 
sometimes cooking them in leaves, but at other times eating them 
alive. (See p. 102.) 

The Annelids are said to give little response to light and shadow 
after they have become accustomed to them. But Copeland, 1930 
(Jour. Comp. Psychol., vol. 10, p. 339), showed that in Nereis virens, 
an apparent " conditioned response " was induced by either in- 
creased or decreased illumination, which indicated to the worm the 
presence of food. The earthworm draws leaves into the burrow to 
line it. There is no exploration of the form of the leaf; it is seized 
at any point, but only those seized at or near the apex get into the 
burrow. 

Hirudinea. — The leeches {Hirudinea) are parasitic forms infest- 
ing invertebrates as well as vertebrates. The majority of the leeches 
live in fresh water and parasitize molluscs and the vertebrates. 
Certain of them are permanent ectoparasites, Branchellion attaching 
to various elasmobranchs. The giant leech {Macrobdella valvidi- 
viana) may reach a length of i>^ feet and is subterranean and 
carnivorous. Clepsine carries its young on the ventral surface. 
The skate sucker {Pontobdella muricata) has a leathery knobbed skin. 
It lays its soft eggs in empty mollusc shells and guards them for 
over 100 days. Lophobdella lives on the lips and jaws of the Cro- 
codilia. Certain intermediate types, the Myzostomata, parasitize 
the feather stars, forming galls on them. 

Parasites of the Annelida. — Certain parasitic Nematodes, the 
minute threadworms {Pelodera pellio), are found in the body cavity 
and nephridia as well as the ventral blood vessels of the earthworm. 
Various protozoa also infect the Annelida. 



ANNELIDA OR ANNULATA 119 

Physiology, Anatomy, and Locomotion.— The Chaetopoda are 
made up of similar segments or metameres. At the sides are borne 
chaetae or setae^ which are in some forms attached to muscular 
processes called parapodia. The well-developed body cavity or 
coelom contains the alimentary canal, the vascular system and 
respiratory branchiae. The excretory organs, nephridia^ are ar- 
ranged in pairs in each segment except the first three and the last. 
Sexes are separate in some forms while others are hermaphroditic. 
The nervous system consists of paired dorsal cerebral ganglia and a 
ventral chain of ganglia with lateral nerves. The larval form is 
called a trochophore . The Naidae are fresh water forms which bud 
asexually. The Hirudinea have 2^o\xX five external annnlations to 
each internal segment and have an extremely distensible crop for 
the storage of blood. They are hermaphroditic. They swim with 
great rapidity. * The aquatic forms have an undulatory movement, 
while the land forms, like the ordinary earthworm, contract the 
circular muscles of the body, thus elongating the segments, and then 
having fixed the setae in the ground, by contraction of the longitu- 
dinal muscles, direct the movement of the worm either anteriorly or 
posteriorly. 

Regeneration. — Earthworms will regenerate a head or a tail, 
sometimes forming a tail in place of the head, and starving to death. 
Grafting and fusion to form two-headed or two-tailed individuals 
have been successful. 

Fossil Relatives. — The Chaetopoda are found as fossils from the 
Cambrian to the present, while the Hirudinea are unknown as fossils. 

Ancestry and Relationship to Other Phyla. — There seems to be a 
well-defined connecting link between the leeches and the allies of the 
earthworm, since we find that the leech Acanthobdella has setae and a 
well-developed coelom. 

There seems to be a wide gap between the Platyhelminthes and 
the Annulata, since both metamerism and a different nervous system 
characterize the latter. Some would hold that the hair worm, 
Gordius^ is a close relative of the Annulata. On account of the 
common Trochophore larva, some have linked the Trochelminthes 
with the Annulata. (See page 125.) 

Economic Importance of the Earthworm 

Positive. — {a) Charles Darwin estimated that there were 50,000 
worms in one acre of ground and cited a stony hill covered with earth 



I20 ANNELIDA OR ANNUL AT A 

three Inches deep In twenty years. Eighteen tons of earth were 
brought to the surface In one acre. 

{b) Earthworms have been and probably are still used by some 
savages as food. 

{c) Earthworms and marine annelids are used as fish bait. 

Negative. — {a) Earthworms may be of slight injury in green- 
house soils. 

{b) Earthworms are accidentally Intermediate hosts in the trans- 
mission of the gape-worm, Syngaynus trachealis. It is not necessary 
to the life of the parasite that it be taken in by the earthworm. 

{c) Certain medical men have from time to time suggested that 
the earthworm may be important in transmitting cancer through 
the deposition of the organism in feces transferred to vegetables by 
the earthworm. This is purely conjectural. 

Economic Importance of the Leech 

Positive. — (a) In cases of hemophilia (persistent bleeding) and 
after contusions, physicians and veterinarians still use leeches to 
extract blood. Some drug stores keep a supply of leeches on hand 
In the spring to serve the needs of those foreigners who get black 
eyes at weddings and other celebrations. The doctor of the Middle 
Ages was called the " leech." 

(b) Leeches are said to have been used for food by some savages. 

Negative. — Leeches parasitize some aquatic and amphibious 
forms. 



CHAPTER VIII 

Phylum Trochelminthes 

The Rotifera, sometimes called "wheel animalcules," belong to 
a group, the exact relationship of which is unknown. They have 
sometimes been classed with the worms. The majority of them are 
free swimming and move by means of a trochal disc (Fig. 51). In 
other forms a telescopic tail aids the animal in performing looping 
movements similar to those of a leech. Przibram states that, in the 
Rotifer, growth is not followed by the formation of new cells, but 
the size of single cells increases. 

Rotifera are for the most part found in fresh water, although 
a few are marine. When the water dries up, the thick-shelled 
winter eggs of certain rotifers may be dispersed by the wind or by 
animals. They are able to survive freezing temperature. 

Eichhorn (1781) describing Floscularia says: "Now I come to a 
very wonderful animal, which has often rejoiced me in my observa- 
tions: I call it the Catcher: extraordinarily artistic in its structure, 
wonderful in its actions, rapid in capturing its prey." (From H. S. 
Jennings, in Ward and Whipple's "Fresh Water Biology," published 
by John Wiley and Sons, Inc., 191 8.) 

Rotifera have an elongated body^ with a tail-like appendage, the 
foot^ which commonly ends in two pointed toes. Pedal cement 
glands aid in attachment. The digestive syste^n is well developed 
with an anteriorly situated inouth which is between the ciliated 
trochal discs and leads into a muscular pharynx. At the lower end 
of the pharynx is the gizzard or mastax which has chitinous teeth. 
(See Gosse, "Structure, Functions and Homologies of the Manduca- 
tory Organs in the Class Rotifera." Phil. Trans., 1856.) 

The excretory system is relatively simple, with paired convoluted 
tubes, the kidneys, which open directly or indirectly into the cloaca. 
The nervous system consists of the dorsally situated brain, with 
nerves given off to the corona, the muscles, integument, and sense 
organs. Two large nerves are given off laterally from the brain 
and each divides into a ventral and a lateral longitudinal trunk. 
The sense organs consist of the tactile and olfacto-gustatory an- 

121 



122 



PHYLUM TROCHELMINTHES 



tennae, and the single or paired eyes, which are not present in all 
forms. 

The male reproductive system consists of a large testis, two or 



.Bristle of 
C orona 



Ciliary Rim. 



Dorsal 

Antenna 



Ciliated Area.\ 

Retractors of 
the Corona 



fsophagus 



Ciliated Area 

CiJ 

A'u clei of the 
yolk Gland 
Ciliated 

Area 
Lateral 
Antenna' 



Intestine 




Sensory 
,:~; Bristle 



Brain 

\\..A/astax 
'^^V^^'\\ Masticatory 
j;. \/V' Apparatus 

%\ j--'\ Gastric Gland 

cJJ — '^ \ Retractors of 

■r^ \ •• the Corona 

^ , • -r \ — Stomach 

^^^■^^r?. >>^- .. . \ . Foot Retractor 

£y.cretory Tube 
Lateral 

/JC I Antenna 

fji. '-•■Contractile 

Bladder 
__ _ Foot Retractor- 

Y!^.— - -ji^- -Cloaca 

■//'-■■■ Cloaca 



Fig. 51. Diagram of a Rotifer. Brachionus rubens Gosse. (After Wesenberg-Lund.) 



four so-called prostate glands, a well-developed vas deferens, a large 
seminal vesicle, and a protrusible penis. 

Males of most Rotifera are relatively short-lived and quite 
degenerate. In some species no traces of the digestive glands and 
mastax, prominent in the female, are found. The rudimentary 



PHYLUM TROCHELMINTHES 123 

anterior portion of the digestive tube serves as a suspensory ligament 
for the testis. (Miller, 1931.) 

Cloacal fertilization is not apparently the rule, since in many 
cases the male apparently bores into the body wall and the sperms 
evidently pass through the wall of the oviduct in order to fertilize 
the eggs. (Gamble, Camb. Nat. Hist.) Males hatch from the 
small eggs of the mictic females. 

In the female the large yolk-gland or vitellarium^ which usually 
consists of eight cells, is found on the ventral side of the stomach. 
The true ovary consists of many small, rounded cells, the posterior 
one enlarged and receiving a shell just before it is extruded. 

Rotifers are especially interesting to us on account of their use 
in experiments on the alternation of parthenogenetic and bi-sexual 
development. Whitney, Shull, Luntz and others have studied the 
influence of food and other factors on the control of the reproductive 
cycle in rotifers (Figure 52).' 

Recalling Loeb's discovery that in the Echinodermata the ex- 
traction of water from the eggs by hypertonic solutions would start 
developmental processes, Jacobs (1909) suggested that in certain 
rotifers desiccation is able to bring on reproduction. Hickernell 
(1917), studying Philodina roseola^ found that the dried rotifer 
had an integument thinner than that of the undried specimen, and 
that an increase in the number of ovarian nuclei occurred at the 
very beginning of the drying process, while the animal was recover- 
ing. But Whitney (1930), reporting on the hatchability of eggs of 
Hydatina senta stored for twenty-two years, found that the fecundity 
of individuals hatching from fertilized eggs after this long period of 
desiccation was lowered, the mothers from old eggs producing an 
average of thirty less daughters than the controls. 

It was shown by dal Bianco (Jour. Exp. Zool., vol. 39, no. i, 
1924) that HCl and FeSOa brought about a notable acceleration of 
the life cycle of Proales felisy even with concentrations that induced 
a marked mortality. 

Jennings and Lynch (1928) studied the origin of individual 
differences during parthenogenetic reproduction under constant 
environmental conditions. Their studies seem to indicate that 
differences in the length of life of rotifers result from the interaction 
of rhythmic processes of digestion and reproduction. They found, 

1 Consult Shull, A. F., Determination of types of individuals in aphids, rotifers 
and cladocera. Biol. Rev., 1929, vol. 4, no. 3, pp. 218-248. 



124 



PHYLUM TROCHELMINTHES 



in addition to difference in length of life, differences \n fecundity of 
individuals, correlated with differences in the size of the partheno- 
genetic eggs from which they were derived. Lynch and Smith 
(1931) showed that in rotifers it is possible to produce and maintain 
depression for a long period of time and that the depression becomes 







Fig. 52. Brachionus militaris. Dorsal views. A, female with attached par- 
thenogenetic female eggs; 5, female with attached parthenogenetic male eggs; C, 
female with attached fertilized eggs; D, male. (After Whitney, Jour. Exp. ZooL, 
vol. 24, Oct. 1917.) 



PHYLUM TROCHELMINTHES 



125 





greater in later generations. With restoration to normal conditions, 
however, it disappears within one or two generations. 

Miller (1931) has described the life history of the rotifer Lecane^ 
which is admirably suited to a study of the alternation of partheno- 
genetic and bisexual generations. The mictic female rotifer, capa- 
ble of sexual reproduction, produces small eggs which if unfer- 
tilized develop into 
males. The fertilized 
eggs are larger and pro- 
duce females. The com- 
mon type of rotifer 
female, the amictic^ can- 
not reproduce by am- 
phimixis (see page 518). 
Eggs of the amictic fe- 
males develop by diploid 
parthenogenesis (see 
pages 503 and 505) and 
produce diploid females, 
which may be either am- 
ictic or mictic. In Mil- 
ler's studies, the length 
of life of females of 
Lecane inermis depends 
to some extent on the Fig. 53. Female producing and male produc- 

Se verity of the process ing eggs of Lecane inermis. Left, the fertilized 
of egg production. The (female producing) egg of the mictic female. Right,, 
/■ , J the (female producing) egg of the amictic female. 

\ Bottom, the (male producing) egg of the mictic 

about two-tnirds as female, before the initiation of cleavage. (Courtesy- 
many eggs as the amictic of H. M. Miller and the Biol. Bull.) 
and have a longer life. 

Parasitisyn in Rotifers. — Some rotifers (Drilophaga) parasitize 
worms and some (Seison) parasitize Crustacea. Others are internal 
parasites found infesting the coelom or the intestine of worms. 

The trochosphere^ or trochophore larvae of the Rotifera, resemble 
the free swimming larvae of certain annelids. (See page 119.) 

References on Trochelminthes 

HiCKERNELL, L. M. 1917. A Study of desiccation in the rotifer Phi- 
lodina roseola, with special reference to cytological changes accom- 
panying desiccation. Biol. Bull., vol. 32, no. 5, pp. 343-407. 




126 PHYLUM TROCHELMINTHES 

Jacobs, M. H. 1909. The effects of desiccation on the rotifer Philo- 
dina roseola. Jour. Exp. Zool., vol. 6, no. 2, pp. 207-263. 

LuNTz, A. 1926. Untersuchungen iiber den Generationswechsel der 
Rotatorien. I. Die Bedingungen des Generationswechsels. Biol, 
Zentralbl., 46: 233. 

LuNTZ, A. 1929. Untersuchungen iiber den Generationswechsel der 
Radertiere. II. Der zyklische Generationswechsel von Brachionus 
bakeri. Biol. Zentralbl., 49: 193. 

Lynch, R. S., and Smith, H. B. 1931. A study of the effects of modifi- 
cations of the culture medium upon length of life and fecundity in a 
rotifer, Proales sordida, with special relation to their heritability. 
Biol. Bull., vol. 60, no. I, pp. 30-63. 

Miller, H. M. 1931. Alternation of generations in the rotifer Lecane 
inermis Bryce. I. Life histories of the sexual and non-sexual 
generations. Biol. Bull., vol. 60, no. 3, pp. 345-381. 

Shull, a. F. 191 1. Jour. Exp. Zool., vol. 10, 191 1, and later papers. 

Wesenburg-Lund. 1929. Handbuch der Zoologie, Bd. 2, L. 50, W. 
de Gruyter & Co., Berlin u. Leipzig. 

Whitney, D. D. 1907. Determination of sex in Hydatina senta. 
Jour. Exp. Zool., vol. 5, pp. 1-26. 

Whitney, D. D. 1916. The control of sex by food in five species of 
rotifers. Jour. Exp. Zool., vol. 20, pp. 263-296. 

Whitney, D. D. 1930. Hatching twenty year old eggs and the reduc- 
tion of vigor in the rotifer Hydatina senta. Anat. Rec, vol. 47, 
P- 354- 



CHAPTER IX 



MOLLUSCOIDEA 

Certain forms known as Brachiopoda and Bryozoa ("Polyzoa" 
of England), on account of their resemblance to Mollusca, have been 
grouped under the Phylum Molluscoidea. 

In 1830, J. V. Thompson separated the Bryozoa from the polyps, 
and called them Polyzoa from their habit of gemmation, and their 
digestive tube. One year later, Ehrenberg changed the term to 
Bryozoa. In 1841, Milne-Edwards created the Phylum Mollus- 
coidea, including it in Bryozoa and Tunicata. Subsequently the 
Tunicata were removed, and in 1 853, Huxley added the Brachiopoda. 

Class I. — The Brachiopoda (Gr. brachion^ the arm; and pous^ a 
foot) are strictly marine, being found in all oceans, and occupy a 
calcareous bivalved shell, the valves of which are dorsal and ventral 
instead of lateral as in the Lamellibranchs. Once rulers of the sea, 
it is supposed that the Brachiopoda or " lamp-shells " were notably 
reduced in numbers by 
boring molluscs. They 
are geologically very 
ancient, Lingula, the 
oldest known genus of 
animals, having changed 
but slightly since the 
earliest Silurian times. 

Class 2. — The B^-yo- 
zoa (Gr. bruon^ moss; 
and 200W, animal) are for 
the most part colonial, 
somewhat resembling 
hydroids. They are 
sometimes stained and 

sold as " air-plants " but Hydrozoa (page 69) are the common 
" air plants." They are found in both salt and fresh water. The 
false coral {Discosoma nidita) is a marine colonial form that encrusts 
shells and stones until it somewhat resembles coral. It is found 
in water at least thirty feet deep. (Mayer.) 

127 




° A 

Fig. 54. Statoblast of CristattUa. (After Allman. 
Courtesy of Macmillan and Co., Ltd.) 



128 MOLLUSCOIDEA 

Occasionally one finds the fresh-water Bryozoa Fredericella and 
Plumatella encrusting masses of vegetation and plant life in " pipe 
moss." They die speedily when water is filtered, or when ground 
water is used. The compound bryozoan Pectinatella alarms some 
pond owners as it increases rapidly, forming a jelly-like mass, some- 
times six feet in diameter. (Figure 54.) Bryozoa are eaten by 
sharks, the cunner (a teleost), and an aquatic mammal, the " black- 
fish." 

References on Bryozoa 

Allman, G.J. 1856. Monograph of freshwater Polyzoa. Proc. Roy. 
Soc. 

BossLER, R. S. The Bryozoa or Moss Animals. Smiths. Inst. Rep. no. 
2633. 

O'Donoghue, C. H. and E. 1926. Second List of Bryozoa from Van- 
couver Island Region. Cont. to Can. Biol., N.S., iii, pp. 47-132. 

OsBURN, R. C. 1912. The Bryozoa of the Woods Hole Region. Bull, 
of the Bur. of Fish., vol. 30, doc. no. 760, pp. 205-266. 

Class 3, Phoronidea. — The Phoronidea resemble the Bryozoa 
in some respects and are usually placed under the MoUuscoidea. 
Phoronidea are sessile marine worms bearing tentacles and living in 
chitinous sand-covered tubes. The body of Phoronis is cylindrical, 
and unsegmented, containing a large body cavity, with mesenteries 
dividing it into three chambers. There are two circulatory fluids, 
a colorless one in the body cavity, and the red hemoglobin-zonx.2\mvi^ 
blood of the closed circulatory system. Phoronis is hermaphroditic, 
the larvae in their metamorphosis passing through a stage called the 
Actinotrocha. A horseshoe-shaped nerve ring is located at the base 
of the tentacles, with two ciliated sensory grooves anterior to it. 



CHAPTER X 



ECHINODERMATA 



EcHiNODERMATA (Gr. ecMnos, a sea hedgehog; derma, skin) Is a 
group of marine animals representing the most highly specialized 
of the radially symmetrical forms, and is further distinguished by the 
presence of a calcareous skeleton, which is sometimes in the form of 
scattered particles or spines, in other cases developed into plates. 
A well-developed coelom points to a high degree of organization. 

Classification 

Class 1. Asteroidea (Gr. aster, a star; eidos, resemblance) pentamer- 
ous; arms not sharply marked off from disc; ambulacral 
groove present. (Starfishes.) 

Class 2. Ophiuroidea (Gr. ophis, a snake; oura, a tail; etdos, form) 
pentamerous; arms sharply marked off from disc; no am- 
bulacral groove. (Brittlestars.) 

Class 3. Echinoidea (Gr. echinos, hedge-hog; eidos, form) pen- 
tamerous; without arms or free rays; test of calcareous plates 
having movable spines. (Sea urchin, sand dollar, heart 
urchin.) 

Class 4. Holothuroidea (Gr. helos, whole; thurois, rushing) long 
ovoid; muscular body wall; tentacles around mouth. (Sea 
cucumbers.) 

Class 5. Crinoidea (Gr. krinon, a lily; eidos, form). Arms gen- 
erally branched and with pinnules; aboral pole usually with 
cirri or sometimes with stalk for temporary or permanent 
attachment. (Feather star, sea lily.) 

Class 6. Cystoidea (Gr. cystis, bladder; eidos, form) — extinct. 
Confined to Paleozoic; extend from Cambrian to Permian 
inclusive with maximum development in Ordovician and 
Silurian. 

Calyx usually stemmed; mouth nearly or quite central 
upon the upper (ventral) surface. From the mouth radiates 
two to five or more simple or branching ambulacra along 
which food particles pass to the mouth probably driven 

129 



I30 ECHINODERMATA 

by numerous cilia. These food grooves may be on outer 
surface and are rarely extended into free branches, the arms. 
Anal opening excentric, often closed by a valvular pyramid. 
Cystoids are the oldest and least specialized group of 
Pelmatozoa (which include cystoids, blastoids and crinoids). 
Class 7. Blastoidea (Gr. blastos^ a bud; eidos^ form) — extinct. 
Confined to the Paleozoic, ranging from the Ordovician to the 
Permian. Calyx ovate, short stemmed or stemless; distinct 
arms absent, existing only as pinnules. Ten spiracles around 
mouth, connected internally with hydrospires. Some have 
a distinct anal opening; in others this is fused with one of the 
spiracles. From the mouth radiate five ambulacra! areas. 

Characteristics 

I. Radially symmetrical; larvae bilaterally symmetrical. 

1. Calcareous skeleton, sometimes in plates which fit into each other 

to form a shell; sometimes in the form of scattered particles 

or spicules. 

3. In many the surface is beset with spines or tubercles. 

4. Never move rapidly in an adult condition; some are fixed by a 

stalk. 

5. Never bud to form a colony. 

6. All marine. 

7. Water vascular system (coelomic in origin) used for locomotion 

and to open bivalve molluscs. 

8. Body cavity well developed in the disc and usually in the arms, 

and separate from the digestive cavity. 

Natural History 

Class 1. Asteroidea. Type of Group — Asterias forbesii. 
Starfish. (Figure 55.) — The starfishes have a star-shaped body, 
with a central disc and five radiating arms, each of which contains a 
prolongation of the body cavity and the organs belonging to the 
digestive, reproductive and water-vascular systems. On the dorsal 
side one finds the anus and the madreporic plate, while on the ventral 
surface the tube feet protrude from five narrow grooves. 

External Anatomy. — The upper (aboral) surface is distinguished 
by the presence of many spines of various sizes; pedicellariae at the 
bases of the spines; a madreporite which is the entrance to a water- 
vascular system; and anus. 



ECHINODERMATA 



131 



The lower surface, usually attached, has a mouth, five grooves 
(ambulacral) with two to four rows oi tube feet extending from them. 

The skeleton is made up of calcareous plates {ossicles) united by 
connective tissue. Ossicles are regularly arranged around the 
mouth and in the ambulacral grooves and often along the sides of the 




Fig. 55. Common starfish. (From Mayer. Courtesy of N. Y, Zool. Soc.) 



arms. The ambulacral ossicles are movably articulated so that they 
can open or close the groove. At the end of the ray the ambulacral 
ossicles end in a median terminal ossicle. There are thus two or 
three rows of movable ambulacral spines. The spines are shoj-t and 
blunt, covered with ectoderfu and arranged in irregular rows parallel 
with the long axes of the rays. They are supported on irregularly 
shaped ossicles. 



132 



ECHINODERMATA 




Fig. 56. Ambulacral plates and pores. 
(W. J. Moore.) 



In the spaces between the ossicles are a number of minute pores , 
the dermal pores^ bearing retractive dermal branchiae or papulae which 
are soft filiform processes and concerned in respiration. The body 
wall is covered with a layer of ciliated epithelium, the epidermis, 
continued over tubercles, spines, pedicellariae, dermal branchiae and 

tube feet. (Figure 56.) 

Musculature. — The arms 
are movable, being supplied 
with muscle fibers in the body 
wall. 

Digestive System. — The 
mouth opens through a short 
passage, the esophagus, into a 
wide sac, the cardiac divi- 
sion of the stomach. This is 
five-lobed (pentagonal), with 
each lobe opposite one of the five arms. The cardiac stomach is 
everted through the mouth. Its retraction is effected by special 
retractor muscles attached at the sides of the ambulacral ridges. 

The cardiac stomach communicates with the smaller pentagonal 
pyloric stomach, which in turn opens into a short conical intestine, 
leading upward to open at the anal aperture on the aboral side of the 
disc of the starfish. The pyloric stomach is extended at its five 
corners to form a pair of pyloric ceca in each ray. Each pair of 
pyloric ceca begins as a cylindrical duct, leading into the pyloric 
chamber. This bifurcates to form two smaller ducts, which give off 
laterally short branches, each connected with many small glandular 
pouches. The glandular pouches secrete juices containing enzymes 
and pass them through the series of ducts into the pyloric stomach. 
The pyloric (hepatic) ceca are productive of a digestive juice 
similar to the pancreatic juice of vertebrates, which converts starch 
into sugar, proteins to peptones and emulsifies fats. Intestinal 
ceca, attached to the intestine, secrete a brownish material, probably 
excretory. 

Water Vascular System. — This remarkable system (Figure 57) is 
used in the starfish for locomotion and in securing its food. It is a 
specialized portion of the coelom. From the madreporic plate, the 
stone canal leads downwards to the ring canal or circular canal. (The 
circular canal bears four pairs of Tiedemann's vesicles and one extra 
opposite the stone canal); from this canal five radial canals pass out. 



ECHINODERMATA 



133 



one into each arm; the radial canals give off side branches from which 
come connecting canals to the tube feet and ampullae. The tube feet 
furnish a means of adhering to smooth surfaces when a vacuum has 
been created by the withdrawing of water into the ampullae. 
Squeezing the ampullae causes the water to distend the tube feet 
and they protrude through the pores. 



Madreporite 
Stone Canol 



Tiedemonn Body 
Circular Cona/ —■ 



/Radial Canol - 



Ampulla 

Connecting Cono/ 



Tube Foot 




Fig. 57. Water-vascular system of the starfish. (Drawn by W. J. Moore.) 



Respiration. — The dermal branchiae are thin-walled finger-like 
sacs that protrude through little holes in the wall of the animal, 
called dermal pores. Dermal branchiae, as the name indicates, are 
for respiration. 

Circulation. — The presence of a well-developed digestive system 
and of a quantity of coelomic fluid renders the blood vascular system 
of less importance. The coelomic fluid contains a number of 
ameboid corpuscles that collect wastes and pass them to the exterior 
by passing along the walls of the dermal branchiae. It is also 
worthy of note that the minute Tiedemann's vesicles on the circular 



134 ECHINODERMATA 

canal of the water vascular system produce ameboid lymphocytes 
that may be quite important. 

The perihaemal system, compared by some to a true blood vas- 
cular system, consists of the axial organ (genital stolon), adjoining 
the stone canal; the oral ring vessel, surrounding the mouth and 
divided by a septum; the perihaemal vessel, divided by a septum, 
and the five radial blood vessels that are found in the rays. The 
perihaemal septum is found to contain gelatinous connective tissue 
and many white blood corpuscles (leucocytes), and is perforated by 
many irregular channels. 

Excretion. — Besides osmotic excretion, the starfish has the ability 
to excrete shells and other wastes from the mouth. Indigestible 
foods also pass through the intestine and out at the anal aperture. 
The ameboid corpuscles of the coelomic fluid aid in excretion. 

Reproduction. — Starfishes are not hermaphroditic, although some 
other Echinoderms are. Each animal produces from paired gonads 
either eggs or sperms. The gonads are situated in the rays with 
their ducts opening on the aboral surface through minute pores on a 
pair of sieve-like plates situated close to the bases of the arms, 
between the rays. During the spawning season the gonads may 
have so many eggs that the starfish will have enormously distended 
rays, and the hepatic ceca may be crowded until they are much 
reduced in size. The eggs are fertilized outside the body, although 
many perish without fertilization having been effected. In one 
year a starfish may have arms two and one-half inches long and be 
ready to spawn. 

Artificial Parthenogenesis. — Norman, Greene, Matthews, Mor- 
gan and Loeb, developed a method of inducing the development of 
unfertilized eggs of echinoderms. Loeb continued the work for 
many years and proved that in the absence of sperms, variation in 
the temperature, the addition of sodium chloride, potassium 
bromide and cane sugar solutions would cause normal larvae to 
develop. For years students in the embryology course at the 
Marine Biological Laboratory at Woods Hole, Massachusetts, have 
repeated the experiments with complete success. Subsequent to 
his echinoderm work, Loeb succeeded in producing fatherless frogs. 
(See page 299.) In nature, echinoderms and some annelids as well 
as plant lice and rotifers normally develop parthenogenetically, that 
is, without the stimulus of sperm. 

Nervous System. — The nervous system consists of the nerve ring. 



ECHINODERMATA 135 

found in the disk, and a radial nerve with branches, found in each 
ray, in the integument covering the ambulacral groove. There are 
also two radial nerve bands forming the deep nervous system, and a 
third set of nerve elements, the aboral or coelomic nervous system, 
extending along the roof of the arm superficial to the muscles. 

Sense Organs. — The tube feet and the spines have tactile nerves 
associated with them and the whole animal is undoubtedly sensitive 
to temperature. At the end of a ray one finds a red spot, the " eye,'^ 
which is sensitive to light. Above it is a process, called the tentacle, 
similar in appearance to the tube feet but without a terminal sucker. 
The tentacles are olfacto-gustatory organs and more important to the 
starfish than the so-called " eyes." 

Behavior. — The starfish senses food and is able to open oysters 
readily. MacBride states that small bivalves are taken completely 
into the stomach of the starfish, the empty shell being later expelled 
through the mouth. 

MacBride quotes Schiemenz as follows: " A bivalve able to 
resist a sudden pull of 4,000 grams will yield to a pull of 900 grams 
long continued. A starfish can exert a pull of 1,350 grams- but must 
raise itself into a hump in order to open an oyster." Turned upon 
its back the starfish ordinarily uses certain rays to right itself. 

Economic Importance. Positive. — Starfish are used to a limited 
extent as fertilizer, and have been extremely valuable in the study 
of embryology, particularly in connection with the problems of 
fertilization. Negative. The starfish injures oysters and other 
molluscs by direct action, opening and devouring them or ingesting 
small ones and expelling the shells from the mouth. One little 
starfish ate over 50 young clams in 6 days (Mead). 

Class 2. Ophiuroidea. — The brittle stars or " serpent stars " re- 
semble the true starfishes considerably, having a star-shaped body 
with a central disc and five radiating arms. They have distinct 
oral and aboral surfaces with the mouth in the center of the disc. 

The arms are slender and tapering, covered with plate-like 
ossicles and lateral spines. The muscular system of the arms is 
highly developed so that rapid movement is effected by their lateral 
sweep. Pyloric ceca and anus are lacking, the madreporic plate is on 
the ventral surface instead of the dorsal, the tube feet are tactile 
instead of locomotor and the ampullae have disappeared. Serpent 
stars secure their food by means of specialized, oral tube feet, two 



136 



ECHINODERMATA 



pairs to each arm. " Brittle stars " have highly developed autotomy 
and the ability to regenerate new arms. (Figure 58, ^^ and 5.) 





Fig. 58. A, serpent star. 5, sand dollar. (From Verrlll.) 



Class 3. Echinoidea. — The sea urchins are not star-shaped, but 
globular. The shell or test is made up of firmly united ossicles 
ranged in rows which run from the oral to the aboral poles. Many 
of the plates bear movable spines which aid in locomotion. Five 

ambulacral plates have openings 
into the egg sacs. There are five 
bands of distensible locomotor 
tube feet beginning near the oral 
opening and running towards the 
aboral pole. The distinctive 
feature of the sea urchin known 
as Aristotle^ s lantern consists of 
five jaw-like structures, each 
bearing a rather large sharp 
white tooth. The intestine is 
quite long and has no radiating 
ceca. Sea urchins are able to 
chisel out solid rock by turning 
round and round. The spines 
of large sea urchins have been 
used as slate pencils by missionaries in the Pacific Islands. 

The sand dollars or " cake urchins'" are flattened and disc-like, 
living near the surface of the sand. The heart urchins or " sea bears " 
bury themselves in the muddy sands for several inches. Under the 




Fig. 59. Purple sea urchin. (From 
Mayer, Seashore Life. Courtesy of N. 
Y. Zool. Soc.) 



ECHINODERMATA 137 

name of " sea eggs," the urchins are sold during the spawning season 
in the Orient. 

Class 4. Holothuroidea. — The sea cucumbers include rather 
small forms which are found in the colder waters, and large tropical 
species. Some of the Holothurians are called sea slugs because of 
their resemblance to a mollusc. Other forms are called cotton 
spinners because they excrete cottony filaments when irritated. 




Fig. 60. Sea cucumber. (Courtesy of Amer. Mus. of Nat. Hist.) 

The sea cucumber has a muscular body wall with a few calcareous 
spicules, a circlet of tentacles around the mouth and five zones of 
tube feet running from mouth to anus. {Synapta lacks tube feet.) 

The alimentary canal consists of a long coiled intestine with a 
muscular enlargement, the cloaca, at the posterior end. Respiration 
is carried on by the cloaca, tentacles, respiratory trees and body wall. 

General Considerations 

In the adult condition, Echinoderms usually creep along the 
sea bottom, for they are all marine. The larvae, however, are 
surface swimmers, or " pelagic." They are gregarious in habits 
and found in all depths. 

Anatomy and Location. — The Echinodermata are radially sym- 
metrical, with an exo-skeleton of calcareous plates or ossicles bearing 
in most cases spines. They have a well-developed alimentary, 
nervous and water vascular system, with a poorly developed vascular 
system. Reproduction is sexual. 

Locomotion in the starfishes is a slow, creeping movement by 



138 



ECHINODERMATA 



^ I 



means of the tube feet. The Holothuroidea utilize their tentacles 
in movement. The brittle stars move by lateral contractions of 
their arms. The Echinoidea move by means of spines and a few 

tube feet. 

Physiology. — In the sea urchin we have the first instance of 
masticatory structures in the invertebrates. The five teeth of the 
" Aristotle's lantern " are extremely powerful. The digestive 
system is extremely efficient as seen in the starfish. (See p. 132.) 
Respiration is carried on by the dermal branchiae. Circulation is 
not well developed and perhaps is not needed with the complicated 
water vascular system. The body fluid, hydrolymph or blood, is 
similar to the fluid in the water vascular system, but is richer in 
albumen. In the sea cucumber, Thyone, the hemoglobin occurs 
in small, very numerous corpuscles. Excretion is carried on by the 
mouth, the dermal branchiae and the intestine. 

Reproduction. — Well-developed gonads are present and sexes 
are separate in many of the Echinoderms. Parthenogenesis occurs 
frequently. (See p. 134.) 

Behavior. — The Echinoderms have well-developed reactions to 
stimuli of touch, light and temperature They also have primitive 
olfacto-gustatory sense. 

Embryonic Development of the Echinodermata. — The eggs of 
Echinoderms divide into 2, 4, 8, 16, 32, 64 cells, each finally be- 
coming a blastula^ then a gastrula^ and finally a larval stage. The 
larvae are bilaterally symmetrical, with an aUmentary canal from 
which later bud two coelomic sacs. These form the body cavity and 
the water-vascular system. The larvae of the different classes 
vary somewhat in structure. Bilateral symmetry is lost in the 
adults except as it is retained slightly in the Holothuroidea. 

Importance of Echinodermata in Biological Research. — During the 
past thirty years, we have seen increased utilization of invertebrate 
forms in research at our marine laboratories. The starfish and the 
sea urchin have been the types used in numerous chemical and 
physiological studies, far-reaching in their significance. Mathews, 
Child, J. Loeb, Tenn/nt, F. Lillie, R. Lillie, Just, Heilbrunn, Glaser, 
Sampson, Woodward, and their associates, have been especially 
active in these studies.^ 

1 See the Wistar Institute Bibliographic Service, and the Journal, Biological 
Abstracts, for references. Also refer to paper by D. H. Tenn^nt, 1929, Studies in 
experimental embryology based on sea urchin eggs. Sc. Mon., vol. 29, no. 2 (167), 
pp. 1 17-124. 



ECHINODERMATA 139 

Echlnoderm eggs are especially convenient for studies on the 
physiological changes occurring during development. Warburg 
found for example that fertilized starfish eggs utilized oxygen eight 
times as fast as the unfertilized ones. Important studies on the 
changes in permeability of eggs immediately following fertilization 
have been made by R. Lillie and more recently by Dorothy Stewart. 

F. Lillie and E. Just believe that the secretions of Arbacia (a sea 
urchin) eggs contain an amboceptor with an ovo-phile side chain 
which combines with the egg and a spermo-phile side chain which 
combines with the sperm. The egg secretion enables the sperm 
to fertilize the egg. (Consult Lillie, F. R. 191 9. Problems of 
Fertilization. Univ. of Chicago Press.) 

But A. E. Woodward finds that it is possible to precipitate from 
the egg secretion by one method a substance which activates the 
sperm, and by another method a second substance which brings 
about parthenogenetic development of the sea urchin egg. Dr. 
Woodward has also utilized iodin (see page 439) as an agent in 
parthenogenesis. (Consult Woodward, A. E., and Hague, F. S. 
1917. Iodine as a parthenogenetic agent. Biol. Bull., vol. 38, 
PP- 355-360.) 

The writer of this text believes that iodin saturates the un- 
saturated fats of the egg, and that increased oxidation causes cell 
division to occur.^ (See papers by Chidester and associates.) 

Parental Care. — In the Asteroidea, the young are sheltered in 
the arms of the adults. One form, Pteraster, has a tent-like brood 
pouch. 

Regeneration. — The Echinoderms have a well-developed charac- 
teristic known as self-mutilation or autotomy. This is most marked 
in many Ophiuroids, some Asteroids and some Holothurians, but 
does not occur at all among the Echinoids. Brittle-stars and star- 
fishes, when removed from water or molested, will sometimes break 
off portions of their arms, piece by piece, to the very base. The 
central disc is entirely capable of regenerating new arms. The sea 
cucumbers frequently eviscerate themselves, escape from their 

2 Iodin has a well-known corrosive action on fats, and it is undoubtedly effective 
m dissolving the fatty pellicle around tubercle bacilli as well as other pathogenic 
organisms treated successfully by cod liver oil. The West Virginia University group 
are treating certain diseases with super-iodized cod Hver oil. Possibly iodin is re- 
sponsible for the protective and curative actions ascribed to other chemicals admin- 
istered in combination with it. 



I40 ECHINODERMATA 

enemies and later regenerate the entire alimentary canal. Mayer 
(Seashore Life) reports that the brittle sea cucumber Synapta lives 
in a ringed sand tube agglutinated with slime. Bands of sand are 
formed and forced down to finally form the tube. Leptosynapta 
breaks itself up into short lengths and then regenerates. 

Fossil Relatives. — Cystoidea are extinct. Their fossils are con- 
fined to the Paleozoic, extending from the Cambrian to the Permian 
with maximum development in the Ordovician and Silurian. The 
Blastoidea, also extinct, are confined to the Paleozoic, ranging from 
the Ordovician to the Permian. The Crinoidea range from the 
Ordovician to the present time, being most abundant as fossils in 
the Upper Paleozoic. The Asteroidea, Ophiuroidea, Holothuroidea 
and Echinoidea have descended to the present, from the upper 
Paleozoic. 

Ancestry and Relationships to Other Phyla. — It has been found 
so difficult to connect the Echinodermata with other Phyla that they 
have been for some time considered relatively isolated. Early 
attempts to link them with the Coelenterata on account of their 
radial symmetry have encountered the objection that the Echino- 
dermata have an extensive coelom or body cavity. They have 
highly developed alimentary and nervous systems not present in 
the lower Phyla. It is now believed that the embryonic history 
of the Echinoderms indicates that they developed from a group with 
bilateral symmetry. The oldest classes of Echinodermata are those 
with the radial symmetry least developed. Thus the stalked Cri- 
noids are considered the ancestors of the free living forms. Crinoidea, 
Cystoidea and Blastoidea represent the primitive type, while radially 
symmetrical Asteroidea, Ophiuroidea and Echinoidea are probably 
descended from the primitive Holothuroidea. The Echinodermata 
are an isolated group, with no living or fossil links. The echinoderm 
larva, somewhat comparable to that of Balanoglossus, called Tor- 
naria (see page 217), has led evolutionists to place the Phylum in the 
series of Invertebrates that are supposed to be progenitors of 
Vertebrates. 



ECHINODERMATA 



141 



Economic Importance of the Echinodermata 



Class 
Asteroidea, 

Echinoidea. 
Holothuroldea. 



Negative 
Attack oysters and clams, open- 
ing shells and devouring the 
soft parts. 



Positive 

Fertilizer. 

Eggs used as food. 

Experimental embryology. 

Roe of sea urchins are eaten. 

Spines are used as slate pencils. 

Several species of sea cucum- 
bers are utilized as food by 
the Chinese under the names 
of trepang or beche-de-mer. 



References on Echinodermata 

Cole, L. J. 1913. Direction of locomotion in the starfish, Asterias 
forbesii. J. Exp. Zoo!., vol. 14. 

Gemmill, J. F. 1 91 2. The locomotor functions of the lantern in Echi- 
nus, with observations on other allied activities. Proc. Roy. Soc. 
Lond., Ser. B, vol. 85. 

Kindred, J. E. 1924. The cellular elements in the perivisceral fluid 
of echinoderms. Biol. Bull., vol. 46, pp. 228-251. 

Paine, V. L. 1926. Adhesion of the tube feet in starfish. J. Exp. 
ZooL, vol. 46, pp. 361-366. 



CHAPTER XI 

MOLLUSCA 

The Mollusca (Lat. mollis^ soft) are bilaterally symmetrical. 
This symmetry is modified by dextral, sinistral, or frontal torsion in 
the adult Gastropoda. While for the most part the Mollusca differ 
from the Annelida and the Arthropoda in being unsegmented, the 
Cephalopoda have certain segmented ducts, and the Amphineura 
are segmented. The majority have an exoskeleton of calcium car- 
bonate, the shell. In general we find that Mollusca are sluggish. 
Many Mollusca are of economic importance (see page i6i). 

Classification 

Class 1. Pelecypoda (hatchet foot) or Lamellibranchiata (leafy 
gills). Clams, oysters, mussels, scallops. Usually bilater- 
ally symmetrical, with two-valved shells, and a two-lobed 
mantle. Abundant in Cretaceous of America. Marine and 
fresh water. 

Class 2. Amphineura (on both sides — a nerve). Chitons, with 
bilateral symmetry, shell of eight transverse calcareous 
plates and many pairs of gill filaments. Ordovician to 
present. Marine. 

Class 3. Gastropoda (belly foot). Snails, slugs, whelks, with a 
spirally coiled shell. Some dextral and others sinistral. 
Cambrian to the present. Abundant since Ordovician. 
Marine and fresh water. 

Class 4. Scaphopoda (boot foot). Tooth shells with tubular shell 
and mantle. Cambrian to the present. Dentalium from the 
Tertiary to the present. Marine. 

Class 5. Cephalopoda (head foot). Cuttle fishes, squids, octopi 
and nautili. Bilaterally symmetrical foot divided into arms 
with suckers. Nervous system is located in the head. 
Nautiloids are first known from the Cambrian rocks; they 
reach their maximum development in the Silurian and decline 
to the Triassic. Marine. 

142 



MOLLUSCA 143 

Characteristics 

1. Mollusca are mostly unsegmented and without jointed ap- 

pendages. 

2. Symmetry is fundamentally bilateral, but in the Gastropoda 

there is superposed dextral or sinistral asymmetry. 

3. The foot is usually for locomotion. 

4. The mantle is a dorsal fold of the body wall which covers the 

animal. 

5. Frequently a shell is secreted by the mantle, but sometimes the 

mantle and shell are absent. 

Natural History 

Class I. Lamellibranchiata. Clams and Mussels. — As a type 
for study either the fresh water mussel {Anodontd) or the clam 
{Venus) proves excellent. Both are bilaterally symmetrical and 
have a well-developed foot. 

The Structure of the Shell. — " The mussel shell consists of three 
layers. The outside horny layer is called the perlostracum; the 
middle prismatic layer is formed from tiny prisms of calcium car- 
bonate separated by thin layers of the horny conchiolin found in 
the perlostracum; the Inner layer Is the nacre or ' mother of pearl * 
which consists of alternate layers of calcium carbonate and conchio- 
lin arranged parallel to the surface. The perlostracum and the 
prismatic layers are secreted from the edge of the mantle, while the 
nacre Is secreted from the whole of the epidermal surface of the 
mantle." ^ 

Externally marking the shell, we find rather prominent depres- 
sions, three or four in number, called lines of growth. Indicating the 
number of seasons of growth. Less prominent depressions, the 
lines being close together. Indicate the number of new edges of the 
shell laid down by the mantle during the course of a single season. 
There are also annual layers of nacre. 

Internal Anatomy. — In both forms we find well-developed ante- 
rior and posterior adductor muscles. These must be cut in order to 
separate the shells. When cut, the dorsal hinge ligament forces the 
valves to gape open. Lining both valves we find the mantle. This 
is adherent to the shell ventrally just Inside the edge, the point of 

1 Parker, T. J., and Haswell, W. A. 1928. Text-book of Zoology. The Mac- 
Millan Co., London. 



144 



MOLLUSCA 



attachment, the pallid linCy being readily seen in the cleaned shell. 
In the hard-shelled clam^ Venus, which has two well-developed 
siphons, we find a posterior invagination under the adductor muscle 
called the pallial sinus. It marks the point of attachment of the 
siphonal muscles. The siphons of fresh water mussels are very 
poorly developed. 




Fig. 6 1. Model of clam. (Courtesy of Amer. Mus. of Nat. Hist.) 

Digestion. — The mouth has two pairs of labial palps, ciliated 
externally; the gullet or esophagus is short. A pair of irregular dark 
brown glands, the liver, surround the large stomach which has in it a 
slender gelatinous rod, the crystalline style. T. C. Nelson (Biol. 
Bull., 1925, vol. 49, no. 2, pp. 86-99) gives three views of the func- 
tions of the crystalline style, (i) It contains amylotic ferments 
which digest starch. (2) Its mucous or viscid secretion holds the 
food long enough for proper digestion. (3) It separates the food 
from foreign particles, acting as a " stirring rod." 

The intestine passes from the posterior end of the stomach to 
the visceral mass, coils parallel to the first portion, then turns 
backwards and proceeds as the rectum through the pericardium and 
above the posterior adductor muscles, finally discharging into the 



MOLLUSCA 145 

dorsal exhalant siphon or cloaca. The wall of the rectum has a 
longitudinal ridge or typhlosole (as in the earthworm). Two similar 
ridges begin in the stomach and are continued into the first part of 
the intestine. An oyster is said to strain 135 liters of water daily 
to obtain its oxygen and food. GaltsofF, P. (1928, Bull. Bur. of 
Fish., vol. 44), has shown that for the North Atlantic oyster the 
maximum flow of water is 3.9 liters per hour at 25° C; for the Gulf 
of Mexico oysters, it is nearly twice as much, 7.5 liters per hour at 
25° C. 

Circulation. — The heart consists of a ventricle., surrounding part 
of the rectum, and two auricles. The ventricle contracts and drives 
the blood through the anterior and posterior aortae. Some of the 
blood goes to the mantle where it is oxygenated and then returns 
to the heart but not to the kidneys. The rest circulates through 
the body and is finally collected by the vena cava just beneath the 
pericardium. From the vena cava, the blood passes into the 
kidneys and gills to the auricles and into the ventricle. Oxygen 
and dissolved food are carried to all parts of the body, CO2 to the 
gills, and other wastes to the kidneys. 

Respiration takes place through the surface of the mantle, and 
by means of a pair of branchiae or gills made up of two lamellae on 
each side, united at the edges except dorsally. A lamella is com- 
posed of gill folds supported by chitinous rods and covered with 
cilia. The cilia of the gills produce a current which sets in through 
the inhalant siphon into the mantle cavity and through the ostia 
and the water tubes into the suprabranchial (epibranchial) chamber 
and out at the exhalant siphon. The ingoing current carries oxygen 
for the aeration of blood, and also brings food such as diatoms and 
Protozoa, which pass into the mouth between the ciliated labial 
palps. The outgoing current carries excreta from the blood and 
feces from the cloaca. 

Excretion. — The nephridia (organs of Bojanus) are a single pair, 
one on each side of the body just below the pericardium. They are 
U-shaped tubes bent on themselves and opening at one end into the 
pericardium and at the other on the external surface of the body. 
There are two parts — a brown, spongy, glandular kidney, and a thin- 
walled non-glandular bladder with ciliated epithelium which com- 
municates with its mate anteriorly by a large oval aperture. The 
kidney receives excreta from the pericardium by cilia. Waste is 
carried out through the exhalant siphon. The bladder receives 



146 



MOLLUSCA 



excreta from the blood. Another excretory organ is the pericardial 
gland or " Keber's organ." It lies just in front of the pericardium 
and discharges into it. It may collect from the kidney; it secretes 
uric acid. 

Reproduction. — The sexes are usually separate. A few forms 
are hermaphroditic and protandrous. The gonads^ situated above 
the foot, are paired masses of tubes which open just in front of the 
renal aperture on each side. Spermatozoa pass out of the dorsal 
siphon of the male and into the ventral siphon of the female. The 
eggs pass out of the genital aperture and lie in the gills. They are 
fertilized there and develop in a modified pouch or marsupium. 
The eggs develop by cell division until in the fresh water mussel a 



Byssus 




SheU ^:".iA; 



Adductor muscle 




tfM^JfD 



Fig. 62. Glochldium of Anodonta. — A, a young mussel or glochidium. (After 
Balfour.) B, the gills of a fish in which are embedded many young mussels forming 
"blackheads." (After Lefevre and Curtis.) (From Hegner, College Zoology. 
Courtesy of Macmillan Co.) 



glochidium is produced. This has a shell with two valves, hooked 
in some species, and closed by muscles. The glochidia attach to 
the gills or fins of a fish, become surrounded by the stimulated 
epithelium of the host, and develop there until able to carry on 
independent existence. They are thus dispersed by the fishes to 
considerable distance. (Figures 62 and ^^?) 

In Venus and many other molluscs, we find that the embryo 
develops as a free swimming larva of the trochophore type called a 
veliger. 

Eggs. — Lamellibranchs have a large number of eggs. The 
oyster has 300,000 to 60,000,000 per annum. The fresh water 
mussel has 200,000. 

Nervous System. — There are two cerebral ganglia (one on each 



MOLLUSCA 



147 



side of the esophagus) with cerebral commissures forming a nerve 
ring. Each cerebropleural ganglion sends a nerve cord ventrally, 
ending in a sin^t pedal ganglion in the foot. Each cerebropleural 
ganglion gives off a cerebrovisceral connective (sometimes enclosed 
by the kidneys) leading to a single visceral ganglion. 




Fig. 63. Different stages of cyst. Proliferation in glochidia, fin margin of carp. 
(After Lefevre and Curtis. Jour. Exp. Zool.^ 19 10.) 

Sense Organs. — A patch of yellow epithelial cells, the " osphra- 
dium," covers each visceral ganglion. They are supposed to be 
olfacto-gustatory organs. Paired otocysts (statocysts) with calcareous 
statoliths behind the pedal ganglia are organs of equilibrium. 
Yves Delage removed the otocysts and caused lack of balance. 
The edges of the mantle have sensory cells — especially on the 
inhalant siphon — which are sensitive to light and touch. Pecten, the 
scallop, has from 80 to 120 ocelli at the edge of the mantle. They 
are connected with the branchial ganglion and each has cornea, 
lens, and optic nerve. Apparently visual organs are absent in the 
fresh water bivalves, but they are better developed in the marine 
forms along shore. There is no satisfactory evidence for color 
vision in Mollusca. Certain eyeless species react to sudden darken- 
ing very quickly, but soon get used to stimuli and cease to respond. 
The sense of geotropism ^ is determined by obscure conditions. 
Reactions are influenced by size of illuminated or darkened surface, 
as well as by intensity of light. 

Class I. Lamellibranchiata. — Fresh water mussels or clams 
( Unionidae, Anodontidae, Lajnpsilidae) have assumed considerable 
importance in America. The United States Bureau of Fisheries has 
established a Biological Station at Fairport, Iowa, for the artificial 

^ See page 25 for definition of tropisms. 



148 



MOLLUSCA 



propagation of mussels in the Mississippi basin. Valuable pearls 
are secured from the adult mussels, and pearl buttons are manu- 
factured from certain mussel shells. Their larvae (glochidia), 
parasitic on the gills and fins of fishes, become dispersed widely. 
(Figure 64, A and .S.) 




Fig. 64//. Unto gibbosus Barnes. (After Simpson, U. S. B. F. Bull., 1898.) 

The sa/f water or edible mussel {Mytilus edulis), cultivated for 
many years in France and England, has only recently come into 
general use in the United States. Through the activities of the late 

Dr. I. A. Field,3 the 
many mussel beds on 
the Atlantic coast are 
now being utilized. In 
mid-summer, mussels 
may sometimes become 
poisonous. 

The " pearl-oyster " 
(Meleagrina), which is 
not a true oyster but a 
mussel, is found in the 
Fig, 645. Lampsilis luteolus La. Female. (After South Sea Islands, Ja- 
Simpson, U. S. B. F. Bull., 1898.) pan, Ceylon, the East 

Indies and the West 
Indies. Pearls are an accumulation of layers of " nacre " laid down 
around foreign substances. (See page 157, Culture Pearls.) 

The softs helled clam {My a arenarid)^ sometimes called the long- 

^Field, I. A. 191 1. The food value of sea mussels. Bull. Bur. Fish., vol. 29. 




MOLLUSCA 



149 



necked clam, is preferred by New Englanders for clam bakes and 
chowders. It has extremely long siphons. The quahog ( Venus 
mercenaria), or hard-shell clam, is found along the entire Atlantic 
coast. Used little at the coast, it is preferred inland as it can be 
shipped long distances and kept alive for a considerable time. Blue- 
lined ones were used as money " wampum " by the American 
Indians (Figure 65, A and B). The giani clam {Tridacna gigas) is 




Fig. 65. y/, soft shell clam, M\a. B, razor shell clam, Ensis. 

Courtesy of The Century Co.) 



(From Arnold. 



found in tropical waters where it sometimes proves a menace to 
divers. Its shell may weigh five hundred pounds and reach a 
length of four feet. A single valve may be found in use as a church 
font. The razor-shell clam {Solen maximus) is eaten by the poorer 
people of the British Isles, but not known in fashionable restaurants. 
The giant " geoduck " clam of the Pacific coast {Glycimeris generosa) 
reaches a weight of six pounds and has a siphon sometimes extended 
twenty-four inches. The West Coast ''little neck" clam {Tapes 
staminea) is an important food. The cockle {Cardium edule) is 
eaten considerably in Europe. It is easily digested. 

The scallop (Pecten irradians) found off-shore on the Atlantic 
coast does not reach a diameter greater than three inches. Its 
single adductor muscle is used for food. The giant scallop {Pecten 
maxijnus) is found in deeper water and reaches a diameter of seven 
inches. Both the scallops are extremely rich in iodine and should 
be utilized more inland since they keep on ice in a much better 
condition than do oysters. The crusaders brought with them from 
the Holy Land a Mediterranean scallop {Pecten jacoboeus) which 
they wore as a badge, indicating their foreign service. 



I50 



MOLLUSCA 



The oyster [Ostred) "* is sessile and lacks a foot. It is used in 
America more than any other shell fish and has been popular in spite 
of the occasional occurrence of typhoid carried by freshened oysters. 
The practice of transporting oysters from relatively clean salt water 
to the mouths oi polluted t'xy&vs and there keeping them " floating " 
until they have become bloated and swollen and have lost their 
true ocean flavor is one that has brought oyster dealers additional 
money when they sold oysters by the quart, but has lost many lives 
from the typhoid germs collected. 




Fig. 66. Mussel with Buddha images. Chidester. {Sci. Am. Supply 191 5.) 



The window-glass shell ( Placuna placenta) is used in the tropics 
for windows in churches and other buildings. Reese reports that 
the demand for " window pane " shell in the Philippine Islands 
has recently exceeded the supply, so that the Philippine Bureau of 
Science planted new beds. 

The wood-boring ship-worms {Teredo and Bankid) were in early 
days a formidable enemy of wooden ships. Recently it was dis- 
covered that the wood-boring ship-worm, Teredo navalis^ was doing 

^ Brooks, W. K. 1905. The Oyster. Bait. 



MOLLUSCA 



151 



great damage to the piles in Pacific and Eastern harbors/ At- 
tempts by the United States Navy to protect wharves and piles 




IS 

Fig. 67. Teredo navalis. Age five weeks from metamorphosis. 6", shell ;F, foot; /j, 
incurrent siphon; es, excurrent siphon;/), pallet. (B. H. Grave, Biol. Bull., Oct. 1928.) 



A 



have resulted in the sheathing of some docks with concrete 

pregnation of the piles with creosote has also 

given a large measure of protection (Figure 

67). The borer {Pholas) is able to penetrate 

rocks and cement. It has extremely long 

united siphons and a shell with a file-Hke 

surface. 

Class 2. Amphineura. (Figure 68.) — The 
chitons are bilaterally symmetrical molluscs 
with eight calcareous plates or shields which 
protect the dorsal surface of their boat-shaped 
body. Like the wood louse and armadillo 
they are able to roll themselves into a ball for 
protection. In some species the shell plates 
have between eleven thousand and twelve 
thousand primitive visual organs. Chitons 



Im- 




Fig. 6 8. Chiton. 
(From Hertwig-Kingsley, 
Manual of Zoology. 
Courtesy of Henry Holt 
&Co.) 



^ Grave, B. H. 1928. Natural history of shipworm. Teredo navalis, at Woods 
Hole, Mass. Biol. Bull., vol. 55, no. 4, pp. 260-282. 

Hill, C. L., and Kofoid, C. A. Marine Borers and Their Relation to Marine 
Construction on the Pacific Coast. Final Report of the San Francisco Bay Marine 
Piling Committee. 1924. 

Sigerfoos, C. P. 1908. Natural History, Organization and Late Development 
of the Teridinidae or Shipworms. Bull. U, S. Bur. Fish., vol. 27, p. 191. 



152 MOLLUSCA 

are found in shallow water, and are used as bait and for food. 
One Pacific coast species reaches a length of eighteen inches. 

Class 3. Gastropoda. — The Gastropoda differ from the Lamelli- 
branchiata considerably, in that they usually have a spirally coiled 
shell consisting of a single piece, a head region with eyes and sensory 
tentacles, and in the alimentary canal have a buccal organ, the 
odontophore^ bearing rows of chitinous teeth and functional in rasping 
food and in cutting through other shells. Gastropoda creep slowly 
on a ventral foot, which in the marine snails carries a horny opercu- 
lum used in closing the orifice when the foot is retracted. 

The chank-shell {Turbinella pyruni) , found in the Indian Ocean, 
is used in the East Indies for bangles. When cut into armlets and 
anklets, chanks are worn by the women of Hindustan. Chank- 
shells were also used for beating cloth. The whelk {Buccinum) is 
eaten by some Europeans. Another whelk {Purpura) was used 
by the ancients in the production of " Tyrian Purple." The 
Romans secured their dyes from shells found off the coast of Tyre 
in Asia, and at Meninge on the shore of Africa. Pliny speaks of the 
mixture of dyes of different shades to produce the finest purple for 
royal robes. The slipper limpets {Crepidula Jornicatd) are de- 
generate scale-like animals that in many cases become attached 
permanently to a stone or dead shell by a stony cement secreted by 
the foot. The embryology of Crepidula was the subject of an 
authoritative study by Conklin (Jour, of Morphology, vol. 13, 1897). 
The common limpet {Patella vulgata) is used as food in England and 
on the Continent much more than in the United States. The ear- 
shells ( Haliotis) found on the Western coast of America appear like 
the single valve of a Lamellibranch, but they are true gastropods. 
The shells are used for the manufacture of ornaments, in inlays 
and also for making buttons. They also yield blister pearls of 
brilliant colors. The fleshy foot of the animal is an excellent food, 
which has been eaten in Europe and the Orient for centuries, and 
furnishes abalone steak in California. It is also dried and shipped 
to the Orient. The cowries {Cypraeidae) are used for ornaments, 
to sink fishnets, and as money. A small species {Cypraea moneta) 
is used in Siam and Western Africa as money. Lankester mentions 
the fact that in the Friendly Islands the orange cowrie, a symbol of 
rank, is worn only by the chief of the tribe. 

The helmet shells {Cassidae) are used in the manufacture of 
cameos^ since either white or black may be carved with the other as 



MOLLUSCA 



^S3 



a background. The tritons or sea conchs {Tritonidae) reach a 
length of twelve inches. The South Sea Islanders use one species 
as a trumpet. 

The common periwinkle {Littorina)^ used as food in Europe, 
particularly the British 
Isles, is not so popular in 
America, although it occurs 
along the Atlantic coast. 

The oyster drill ( Uro- 
salpinx cinereus) is an im- 
portant enemy of the 
Lamellibranchs. Using its 
" radula " it quickly bores 
holes into the hardest shell. 
(Figure 69, A and B.) 
The drilling sea snail 
{Natica heros) deposits its 
eggs in a " collar " com- 
posed of sand, agglutinated 
by mucus. The land snail 
{Helix pomatia)^ imported 
from Europe, is sold in 
large cities and considered 
a delicacy. The American 
Helicidae are smaller in 
size and are considered by 
some vegetable gardeners 
to be quite injurious to 
plants. The escaped Euro- 
pean garden snail is very 
destructive to certain veg- 
etables and flowers. Pliny 
speaks of snails, cultivated 
by the Romans, with shells 
that would hold a quart of 
wine! The modern snails are not more than three or four inches 

lo"g- ^ . ... 

The common pond snails include the genus Limnaea with its 

shell a right-handed spiral, which lays its eggs in the spring in 

capsules covered with jelly; and the genus Physa (in which the 




Fig. 69. Enemies of the oyster. A, Uro- 
salpinx, the drill; B, Fidgur, the whelk. 
(From U. S. B. F. Report, 1897.) 



154 



MOLLUSCA 




spiral is a left-handed one), which attaches its egg capsules to sticks 
and leaves in the water. Either form is excellent for the study of 
embryonic development, since the eggs are deposited in laboratory 

aquaria and develop rapidly. (Figure 70, A 
and 5.) 

The land slugs {Limacidae) have a vestigial 
shell. A species found in California reaches the 
length of twelve inches. The giant slug {Arioli- 
?nax sp.) is used by the South American Indians 
in the manufacture of " bird lime " to capture 
Fig. 70. Left, hummingbirds. 

Lymnaea with dex- om c ^ '^ j J*1*~ 

^ , , ,, „. , ^ Snails are of great sanitary and medical sig- 

tral shell. Right, , r . 1 j •.• 

Physa with sinistral nincance as hosts ot larval trematodes, parasitic 

shell. in vertebrates, including man. (See p. 77.) 

Class 4. Scaphopoda. — The tooth shells or 

tusk shells have a tubular calcareous shell open at both ends. The 

foot is at the larger end. A lingual ribbon (radula) is present, and 

the animal has a rudimentary head. Tentacles, eyes, a heart and 

gills are absent. The captacula are ciliated contractile filaments 

perhaps for breathing and securing food. The animal has the 

univalve shell and radula of the Gastropoda and the symmetry 

and pointed foot, without tentacles or head, that characterize the 

Lamellibranchiata. 

The Dentalium or iusk shell was used in California among the 
Indians and the early whites as currency. The shells used were 
valued at ^5.00 each if about two and one-half inches long; smaller 
ones were about one inch long and were worth about ^oi. An eleven- 
shell string was worth about I50.00. Dentaliums were traded for 
wives, clothing, furs, and woodpecker scalps, whose red topknots 
were of considerable value also. 

Class 5. Cephalopoda. — The Cephalopoda, which include the 
squids, sepias and octopuses, are highly developed marine Mollusca. 
They have a true head, with well-developed eyes and olfactory 
organs, and the anterior portion of the foot is modified into tentacles 
or arms. The body is bilaterally symmetrical. Locomotion is 
accomplished by movements of the tentacles and by expulsion of 
water from a funnel or siphon leading out from the mantle cavity. 
The shell is usually internal, that of the cuttlefish being sold as 
" cuttle-bone," but in the Nautilus, the shell is highly developed as 
a chambered external coiled structure. 



MOLLUSCA 



HS 



The cuttlefishes^ or Sepias, have ten arms and a pair of highly 
developed eyes. The body is covered by the mantle. Cuttle- 
bone comes from the inner shell, which is very porous and light in 
weight and largely lime. Cuttlefishes furnish sepia ink which is 
used in art. Ground cuttlebone called " pounce " is used somewhat 
in medicine as an anti-acid and when powdered fine is used by 
draftsmen to prevent blotting. Italians esteem the " sepias " a 
delicacy. India ink is made from the ink bags of fossil cuttlefishes. 

The octopus {Octopus vulgaris) bears eight arms. It may reach 
a length of fifteen feet and weigh seventy-five pounds. Terrible 
stories are related (at a few dollars a column) regarding the battles 
of divers with these horrible " devil fishes." They are used for 
food by the Chinese and Italians. 




Fig. -jiA. Female Argonauta argo. (Lull, Organic Evolution, after Claus-Sedgwick. 

Courtesy of Macmlllan and Co., Ltd.) 

The squid (Loligo) reaches a length of about one foot. The 
internal shell, called the " pen " on account of its resemblance to a 
feather, is relatively thin and chitinous (horny), not calcareous. 

6 The Arctic cuttlefish is said to reach a length of eighteen feet, its size being ap- 
parently correlated with the greater abundance of diatoms and other food in the 
plankton of northern waters. 



156 



MOLLUSCA 



Giant squids may reach a total length of thirty feet, the body being 
not more than ten feet long. They form the food of the sperm 
whales. Squids are used for bait and are eaten by French, Italians, 
and the Orientals. Squid oil has been used for lubricating, and by 
the Chinese as a medicine. 

The chambered nautilus {Nautilus pompilius) is a cephalopod 
with a many-chambered, spiral shell, lined with beautiful pearly 
nao'c. Unlike the squids and octopi, the nautilus lacks an ink sac 
and cannot change its color. Oliver Wendell Holmes' celebrated 
poem has immortalized " The Chambered Nautilus." 

The paper nautilus {Argo- 
nauta argo) with a thin shell is 
more active than the chambered 
variety and is frequently seen 
near the surface of the ocean. 
The females are pelagic during 
breeding season, but are found 
in the depths the rest of the 
time. The male Argonaut, one 
inch long, only i/io of the size 
of the female, has no shell, and 
is able to detach the third arm 
on the left side laden with sper- 
matophores and spermatozoa. 
The entire " hectocotylized 
arm " passes into the mantle 
cavity of the female and, at- 
FiG. 7i5. Male Argonanta showing taching, permits the spermatozoa 
hectocotylized arm. (Lull, Organic Evo- ^^ fertilize her eggs. (Figure 71, 

A and B.) 

Pearls. — Since so much of 
the reputation for economic importance of the Mollusca depends 
on the value of pearls, let us consider the source of pearls and 
the methods used in producing " culture pearls." 

Composition. — The composition of pearls is 91.72 per cent 
carbonate of lime, 5.94 per cent organic matter and 2.34 per cent 
water. 

Source and Value. — The pearl " oyster," one of the Aviculidae, 
Margaritifera, is not an oyster but a mussel. It is found in the 
Persian Gulf and off the coasts of Ceylon and Japan. Similar forms 




lution, after Claus-Sedgwick. 
of Macmillan and Co., Ltd.) 



Courtesy 



MOLLUSC A 157 

have been found in the Philippine Islands and on the coasts of 
Venezuela and Pacific Mexico. Black pearls from the " pearl 
oyster " of the Gulf of Mexico are extremely valuable. The fresh 
water mussels, besides furnishing pearl buttons, also produce a 
fine quality of pinkish pearls. The abalones {Haliotis) found in the 
Pacific Ocean produce very few good blister pearls but the shells are 
valuable for mother of pearl. Pink pearls are sometimes secured 
from the large West Indian conch shell, Strombus gigas^ one of them 
having sold for five thousand dollars. 

True pearls increase in value notably according to the size. If 
a one-grain pearl is worth ^10.00, a two-grain pearl is worth ^40.00, 
while a ten-grain pearl is valued at ^1,000.00. 

Culture Pearls. — The nucleus of a pearl may be a parasite, an 
ovum, a fragment of tissue, or a bit of shell or other hard material. 
Investigators have found Cestode larvae, Trematode worms, and 
even small Crustacea and Hydrachnids as the nuclei of pearls. 
Centuries ago the Chinese discovered that if foreign substances were 
placed between the mantle and shell of a mussel, in many cases a 
coating of " mother-of-pearl " was laid down over the insert. 

The Japanese developed the earlier work of the Chinese to a 
great enterprise under the guidance of the late Prof. Mitsukuri, 
opening the oysters slightly and inserting bits of sand, images, and 
bits of mother of pearl, with the result that blister or culture pearls 
were produced. In 1892, Kokichi Mikimoto, the " Pearl King," 
following the suggestions made to him by Professor Mitsukuri, 
began the cultivation of pearls on a large scale. Mikimoto's oyster 
beds extend over 40,000 acres. According to Jordan (1927) he 
employs one thousand people. The divers are all young women who, 
it is reported, can remain two minutes under water. 

Culture pearls with a spherical mother-of-pearl nucleus are just 
as aesthetic as a natural pearl, which may be the " sarcophagus " 
of a tape-worm. In spite of attempts to bar them from the market 
as genuine, they are now sold for as much as $200 each. Chemically 
and biologically they are true pearls. 

Coated Glass Substitutes for Pearls. — Alabaster or glass beads 
are now coated with pearl essence secured by the extraction of 
guanin crystals from herring and other fishes (see page 254) and are 
sold as artificial pearls. 




158 MOLLUSCA 

References on Pearls 

Chidester, F. E. 191 5. Artificial production of pearls. Sc. Am., 

Supp. No. 2043, Feb. 1 91 5, p. 140- 
Jordan, D. S. 1927. Mikimoto and the culture pearls. Sc. Am., Oct. 

I927> PP- 300-302. 
Tressler, D. K. 1923. Marine Products of Commerce. N. Y. 

General Consideration of the Mollusca 

Distribution. — Mollusca are found in both fresh and salt water, 
and on land. While they are usually free-living, they serve as 
obligatory intermediate hosts in the development and transmission 
of certain parasitic worms, such as the lung and blood flukes of man, 
and are also found in association with some of the aquatic Crustacea, 

Physiology. — The soft bodies of the molluscs are protected by a 
slimy covering frequently supported by a shell. Certain of the 
gastropods and cephalopods lack such a shell. 

In the Lamellibranch, Pecten^ the two valves are rapidly opened 
and closed and the animal flaps along at considerable speed. Other 
forms like the long-necked clam {Myd) utilize their siphons in bur- 
rowing while the majority move slowly by means of the foot. The 
oyster is sessile in the adult condition. In certain Gastropoda there 
is a slow wave-like muscular motion of the foot; whereas in other 
species locomotion is accomplished by ciliary activity (Copeland ''). 
The Cephalopoda when undisturbed move slowly by means of the 
tail fin and sometimes by " walking " on the arms, but they are 
capable of very rapid backward movement by jets of water ejected 
from the " funnel " or siphon. 

The Mollusca have a well-developed body cavity usually divided 
into two chambers, the pericardial and the visceral. Digestion is 
facilitated by the secretions from the hepato-pancreas or " liver." 
The Gastropoda have a highly developed lingual ribbon, the 
" radula," which is instrumental in the penetration of hard shells. 
Snails are able to digest cellulose without the aid of bacteria. In 
Cephalopoda a salivary secretion is poisonous enough to paralyze 
small crabs. The devil-fish or octopus has acid-secreting glands 
which soften the shells of oysters at the point of drilling. Teredo 
feeds in part on the wood from its burrows filed off by its shell. 

" Copeland, M. 1919. Locomotion in two species of the gastropod, Alectrion. 
Biol. Bull., vol. 37, no. 2, pp. 126-138. 



MOLLUSCA 159 

Many of the snails respire by means of air taken into the mantle 
cavity which functions as a lung. Other aquatic forms breathe by 
means of gills. Pinna-globulin is a pigment in the blood of the 
Lamellibranchs. Pinna squamosa has manganese instead of the 
copper common to invertebrates, including oysters, but it does not 
appear to function in transporting oxygen. 

Many gastropods and cephalopods have haemocyanin, and in 
the Gastropod Planorbis, haemoglobin occurs. (Redfield, personal 
communication.) 

Nervous System. — The nervous system of the MoUusca consists 
of cerebral, visceral and pedal ganglia, with connectives. In the 
Gastropoda, the coiled shell causes the nervous system to be in a 
spiral. 

It is said that the smallest snail can withstand more strychnine 
than an adult man. Richards has shown « that Mytilus is poisoned 
readily by atropine and camphor and less so by caffeine. 

Regeneration. — Autotomy is not characteristic of moUusca in 
general, but a few Lamellibranchs and Gastropods are able to part 
with and regenerate a new bit of their foot. 

Growth Studies on the MoUusca. — Molluscs are especially 
suited for studies of the growth of animals because the shell is added 
to and extended by the mantle as the organism grows. The amount 
added in a given time, or the rate of growth, depends on the amount 
of food that the animal receives. During the winter the animals 
get little food and the edge of the shell thickens leaving a growth 
ring or check mark when the growth begins again early the next 
spring. 

On Cape Cod, Massachusetts, the growth of the edible mussel 
{Mytilus) begins in March following the great increase of its food 
(plankton) in January and February .^ The growth rings of the 
Pacific Coast razor clam {Siliqua) appear very clearly so that 
Weymouth i" and his associates have been able to extend our views 

8 Richards, O. W. 1929. Conduction of the nervous impulse through the pedal 
ganglion of Mytilus. Biol. Bull., vol. 56, pp. 32-40. Richards has shown that the 
rate of conduction of the nervous impulse was 92.9 ± 2-2, cm. per second in Mytilus 
edulis at 24° C. 

9 Richards, O. W. Studies on the growth of M. edulis and calijornianus in progress 
communicated personally to the author. 

10 Weymouth, F. W., and McMillin, H. C. 1930. Relative Growth and Mortality 
of the Pacific Coast Razor Clam and Their Bearing on the Commercial Fisheries. 
Bull. U. S. B. F., vol. 46, pp. 543-567- 



i6o 



MOLLUSCA 



of the nature of the growth process from the analysis of measure- 
ments of the growth of this clam. Other forms do not show these 
rings clearly so that Richards has used x-ray pictures to show the 
internal structure of the shell not visible to the unaided eye. The 
growth of many shells takes place in an orderly manner and in some 
cases in precise mathematical form such as the logarithmic spiral 
formed by the chambered nautilus. ^^ 

Embryology. — The eggs of the MoUusca are extremely numerous. 
In the oyster, it is estimated that there are 60,000,000; in the squid 
as many as 40,000. The sexes are usually separate except in the 
Gastropoda. (Figure 72.) 



\ 



■v, ■-. 







[ 






/ 



Fig. 72. First stages in embryonic development of the pond snail {Lymnaeus): 
fl, egg cell; b, first cleavage; c, second cleavage; d, third cleavage; e, after numerous 
cleavages (Morula);/, blastula (in section); |", gastrula just forming (in section); h, gas- 
trula completed (in section). (After Rabl.) This may be taken as a type of the 
earliest development of all many-celled animals (Metazoa). (From Jordan and Kel- 
logg, Animal Life. Courtesy of D. Appleton and Co., Publishers.) 



Most larval molluscs include a trochophore stage, which becomes 
a veliger larva. The velum is situated anteriorly to the mouth and 
proves extremely important in the locomotion and dispersal of the 
animal. In the fresh water mussels, a parasitic stage, the glochidium 
(see page 148) attaches to the gills or fins of fishes. 

Care of the Young. — In certain of the Gastropoda, the eggs hatch 
within the body of the parent. In one form the female {Galerus 
chinensis) hatches her eggs by keeping them between her foot and 

" Thompson, D. A. W. 1917. Growth and Form. Camb. Univ. Press. 



MOLLUSCA 



i6i 



the stone to which she adheres. The octopus broods her eggs, 
renewing the water around them by siphonal jets. 

Fossil Relatives. — As indicated on page 1 42, under Classification of 
Mollusca, they are found from the Cambrian to the present, the La- 
mellibranchs being especially abundant in the Cretaceous of America. 

Ancestry and Relationship to Other Phyla. — On account of the 
occurrence of the trochophore larva the Mollusca are linked with the 
worms. The Cephalopoda are separated from the other Mollusca, 
having no free larvae and being provided with highly developed eyes 
and nervous system. 



Economic Importance of Mollusca 

Class Positive 

Lamellibranchiata. i. As money. Quahaugs and cowries, i. 

1. Pearls. Pearl oysters, clams and 
mussels. 

3. Buttons from mussel shells. 

4. As ornaments. 

5. Food — oyster, clam, mussel, scallop 

(adductor muscle), shells as chick- 2. 
en grits. 

6. For roads (New England uses oyster 

shells). 

7. As church fonts — Tridacna (500 lb. 

shells). 

8. Window pane (Placuna). 



Negative 

a. Pholas — "borer." 
b. "Ship-worms." 
Teredo navalis and 
Bankia fimbriata 
attack wooden 
ships and piles. 

Giant clam. Tridac- 
na gigas (enemy of 
divers). 



Gastropoda. 



I. For food or bait. Whelks, periwin- 
kles, top shells, limpets, the aba- 
lone (Haliotis). 

1. For buttons and as ornaments. 
Ear shells, sea snails, cameo shells 
(Cassis), top shells. Queen conch 
shells {Strombus gigas) were for- 
merly used in Liverpool for the 
manufacture of porcelain. 

3. For dye stuffs the "sea hare" fur- 

nishes purple dye. "Tyrian pur- 
ple" {Purpura, the whelk). 

4. For bird lime. The giant slug is 

used by South American Indians 
to lime humming birds. 

5. The calcareous front doors (oper- 

cula) of some S. American gastro- 
pods are sold for use in the U. S. as 
"eye-stones." 



1. Boring gastropods at- 
tack lamelli- 
branchs. 

1. Destroy vegetables 
and plants — gar- 
den snail (slug) 
Limax. 

3. Sometimes snails at- 

tack the eggs of 
fish in nests. 

4. Intermediate hosts of 

larval stages of 
flukes of man. 



l62 



MOLLUSCA 



Amphineura. 
Scaphopoda. 



I. Chiton used as food and for bait. 



I. Tusk shells (Dentalium) were used 
as currency in California by the 
Indians. 



Cephalopoda. 



I. Little known except 
in fiction. 



1. Sepia "bone" and "cuttle bone" 
used to feed birds requiring lime. 

2. Dr. J. A. Eiesland cites the use of 

cuttlebone for erasers in Norway 
about 1870. 

3. "Pounce" as anti-acid (medicine); 

in art work to prevent blotting. 

4. Sepia — for ink. 

5. Squid oil — medicine and as lubricant. 

6. Food and fish bait. Squids, octopi 

and sepia. 

References on Mollusca 

Cooke, A. H. 1895. Mollusca, in Cambridge Natural History, Mac- 

millan Co. 
Gould, A. H. 1870. Report on Invertebrata of Massachusetts. 2d ed. 

Binney (Mollusca and Tunicata). 

Johnson, M. E., AND Snook, H. J. 1927. Shore Animals of the Pacific 
Coast. The Macmillan Co., N. Y. 

Simpson, G. B. 1901. Anatomy and Physiology of Polygyra albolabris 
and Umax maximus, etc. New York State Educational Depart- 
ment. 

Tressler, D. K. 1923. Marine Products of Commerce, N. Y. 

Verrill, a. E. 1882. Report on the Cephalopods of the Northeastern 
Coast of America. Report of U. S. Fish Commission for 1879. 
Government Printing Office. 



CHAPTER XII 



Arthropoda 



The Arthropoda (Gr. arthron^ a joint; pous^ a foot) include 
more than one-half the number of species in the animal kingdom 
and comprise a wide variety of forms, with great significance econom- 
ically. 

The body, segmented and bilaterally symmetrical as in the 
Annelida, is covered by a chitinous exoskeleton. The heart is 
usually elongated and the nerve cord is ventrally situated, while 
the cerebral ganglia are dorsal and anterior as in the earthworm. 

This Phylum includes insects, barnacles, crabs, crayfishes, 
spiders, ticks, and scorpions. The bee is an example of a beneficial 
form; the housefly, of an injurious type. 



Classification 



Class 1. Crustacea. 

Class 2. Onychophora. 

Class 3. Myriapoda. 

Class 4. Insecta. 

Class 5. Arachnid a. 

Characteristics 

1. Marked metamerism. 

2. Appendages jointed. 

3. Body covered by chitinous exoskeleton, secreted by cells beneath 

it. 

4. Bilateral symmetry. 

5. Mouth and anus at opposite ends. ' 

6. Seldom ciliated. 

7. Muscles usually striped. 

8. Dorsal heart, with incomplete circulatory system, the blood 

sinuses extremely important. 

9. Nervous system includes a ventral nerve chain with ganglia and 

paired dorsal cerebral ganglia. 



164 



ARTHROPODA 




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ARTHROPODA 165 



Natural History 



Class I. Crustacea. — Crustacea vary in size from microscopic to 
the 34-pound lobster. Nearly all have a hard exoskeleton. They 
shed this and grow for a time. Young crayfishes and lobsters 
moult 8 times the first year, 5 times the second year, 3 times the 
third year and from one to three times annually, thereafter. They 
are divided into the head, thorax and abdomen. The head and 
thorax are frequently fused to form a cephalothorax. There are 
usually 21 segments in higher Crustacea. Seven is the typical 
number of abdominal segments. There are eight in the cephalo- 
thorax (5 legs and 3 appendages) and six in the head. 

Subclass Malacostraca. Order Decapoda. Type — Lobster or 
Crayfish. (Figure 73.) Digestive System. — This consists of the 
esophagus, cardiac stomach, pyloric stomach, intestine, and liver. 
The esophagus is lined by chitinous cuticle and supplied with small 
" salivary " glands. The cardiac stomach contains the gastric mill, 
which is equipped with powerful chitinous teeth, the most important 
being the two laterals and the single dorsal. The posterior pyloric 
stomach has a sieve-like strainer of coarse hairs. The short mid-gut 
receives the secretions from the lateral liver or hepato-pancreas. 
This gland absorbs peptones and sugar, manufactures glycogen and 
furnishes enzymes corresponding to the gastric and pancreatic 
juices of mammals. The intestine is long and straight, except for a 
slight dilatation in the sixth abdominal segment, the rectum. An 
intestinal cecum is dorsally situated. Chitin-lined, the intestine 
has but few glands. Both mouth and anal opening are ventrally 
situated. 

Circulatory System. — The blood is a colorless liquid with amebo- 
cytes. In Crustacea., hemoglobin is replaced by a fluid containing 
copper instead of iron, which is called haemocyanin. It is colorless 
when flowing, but turns plumbago colored when exposed to the air. 
The heart is shield shaped with three pairs of ostia. There are seven 
arteries and many sinuses. The ophthalmic artery supplies the 
esophagus, stomach and head. Two antennary arteries supply the 
stomach, antennae and excretory organs. Two hepatic arteries 
supply the digestive glands. There are also dorsal abdo?ninal arteries, 
the sternal artery which passes through the spinal cord, the ventral 
thoracic, and the ventral abdominal. 

Circulation of the Blood.— The heart sends the blood to the 
arteries, capillaries, sternal sinus, and to the^///j where it is purified. 



1 66 ARTHROPOD A 

It returns from the gills to the cardiac sinuses, pericardial sinus and 
back through the ostia to the heart. There are valves in the arteries 
and sinuses. 

Respiration is by means of gills. Astacus, the crayfish found 
west of the Rockies, has i8 pairs; the lobsters have 20 pairs and 
Cambarus, east of the Rockies, has only 17 pairs. 

Excretion. — Paired, flattened " green-glands " are found in the 
ventral region of the head near the esophagus. 

Reproductive System. — Ordinarily the sexes of the lobster and the 
crayfish are separate, although Turner has recorded many interesting 
cases of hermaphroditism in the crayfish. The essential organs of 
reproduction in the male are the bilobed testis, the paired vasa 
deferentia transporting the sperms to the outside, and the modified 
abdominal appendages, called stylets, which are used to transfer 
the spermatozoa to the ventral pouch (seminal receptacle) of the 
female. 

In the female, the bilobed ovary sends off eggs which pass from 
the paired oviducts and are fertilized by spermatozoa stored in the 
ventral pouch at the time of conjugation, sometimes months pre- 
viously. A lobster from 8 to 10 inches long produces from 3,000 
to 100,000 eggs in a season. The crayfish may produce 2,000 eggs in 
a season. Each egg is attached to one of the swimmerets and 
hatches in about two months, the larvae undergoing two or three 
moults before they leave the mother, and moulting 8 times the first 
summer. 

The Nervous System consists of a l^rain (two cerebral ganglia) 
and a ventral nerve cord with esophageal connectives uniting the 
cerebral ganglia and the nerve cord in the sub-esophageal region. 

The ventral cord shows by the great number of concentrated 
lateral nerves as well as by the marked enlargement in the anterior 
thoracic region that the right and left halves of the ventral cord 
have fused. To a limited extent this fusion is evident in the ab- 
domen. 

The ganglia of the last three cephalic and the first three thoracic 
segments have united forming a large compound sub-esophageal 
ganglion. Between the fifth and sixth thoracic ganglia the ventral 
nerve cord is separated widely to permit the passage of the sternal 
artery which runs dorsi-ventrally. There are 12 ganglia belonging 
to the nervous system. The brain supplies the eyes, antennae and 
antennules. (Figure 74.) 



ARTHROPODA 



167 



Senses of the Crayfish. — Touch is the most 
valuable sense. Crayfish are sensitive, to touch 
over the whole body, especially on the chelae 
and chelipedsy mouth parts, the ventral surface 
of the abdomen and the edge of the telson. 

Vision. — The compound eyes are almost 
worthless for detecting the forms of stationary 
objects, but good for moving objects. The re- 
sponse is not due to any change in the intensity 
of light such as that caused by a shadow falling 
on the animals, for they react to a movement 
made on the opposite side of them from a 
window. Crayfish are sensitive to a strong light 
and hide during the day under stones, among 
the roots of plants near the bank, or burrow 
into the bank. They retreat from a strong 
light, but approach a dim one. 

Smell and Taste. — Bell applied meat juice to 
various parts of the body of the crayfish and 
found that the antennae^ antennules, mouth 
parts and chelipeds were especially sensitive. 

Holmes and Homuth found that the outer 
rami of the antennules bearing the olfactory 
setae were especially sensitive to olfactory 
stimuli, that the inner rami of the antennules 
and the antennae^ the mouth parts, and the tips 
of the chelipeds were all sensitive to some extent 
to olfactory stimuli. Crayfish have a highly 
developed topochemical or contact-odor sense. 
The crayfish is sensitive to food when not in 
contact with it. Experiments with freshly cut 
meat and with meat on which the cut surfaces 
had dried showed that the crayfish prefers fresh 
meat, probably because it locates it sooner. 

Hearing. — Bell learned that the crayfish has 
no sound reactions, but is sensitive to vibrations 

Fig. 74. The central nervous system of the lobster. 
(After Calkins, Biology. Courtesy of Henry Holt & Co.) 





1 68 ARTHROPOD A 

in the water. Huxley said, "the crayfish has nothing to say to 
himself or anyone else." 

Equilibrium. — Bunting found that young crayfish with the stato- 
cysts removed would swim upside down as readily as right side up. 
It is also pretty certain that older crayfish have a sense of equilib- 
rium, although the response to rotation in their case is not definite, 
but purely individual. 

In an experiment by Kreldl, shrimps recently moulted and lack- 
ing statoliths were placed in filtered water and furnished iron filings 
which they at once popped into their statocysts. By means of an 
electromagnet he directed their movements, the animals orienting 
according to the combined forces of the magnet and of gravity. 

Eyes. — The compound eyes have about 2,500 visual rods, called 
ommatidia. 

Food of the Lobster and Crayfish. — Lobsters eat conchs, /^cotypus 
(oyster drill), dead and live fish, eelgrass and My a arenaria (the long- 
neck clam). In order to secure hard-shell clams ( Venus) they must 
dig holes 2 feet in diameter and 6 inches deep. Crayfish are omniv- 
orous. Some crayfish eat a great deal of vegetable matter; one 
species, the chimney builder, Cambarus diogenes^ seeming to prefer 
it. The vegetable matter eaten consists of dead leaves, potato, 
onion, young corn and buckwheat. The animal food consumed by 
the crayfish consists of worms, insects, insect larvae, a few fish, frog, 
toad and salamander eggs, and occasionally a dead fish or frog. 
Both lobsters and crayfish are cannibalistic. Sometimes females 
eat eggs from their own abdomens and devour their own freed 
offspring. 

Enemies. — The chief enemies of the lobster, besides man, are 
the codfish, trematodes, and gregarines. The gregarine protozoan 
Porospora gigantea is a parasite on the lobster's intestine reaching 
a length of two-thirds of an inch. The crayfish suffers from internal 
and external enemies. Among the plants which live with the cray- 
fish are diatoms, bacteria and saprolegnia. Internally, Distoma 
cerrigerum and Branchiobdella have been noted. Besides man, 
many small animals find crayfish palatable. 

Many fish, including the black bass, Micropterus, which fisher- 
men find very partial to crayfish, eat them. Surface reports that 
the salamanders Cryptobranchus allegheniensis and Necturus 
maculosus are among the chief enemies of the crayfish. Ortmann 
mentions seeing the water snakes, Natrix sipedon and A^. lebens. 



ARTHROPOD A 169 

when captured, disgorge crayfish and has found garter snakes, 
Eutaenia sirtalis, in the holes of Cambarus tnonongalensis. The 
common box turtle catches many crayfish. Many birds, including 
the eagle, king-fisher, wild ibis and turkey, have been observed with 
crayfish in their claws; or the remains have been seen at the nests. 

Economic Loss from Crayfish. — The river species do not espe- 
cially injure human interests except in occasionally capturing a few 
toads, fish and frogs, but the burrowing species are cited by Ortmann 
as being very injurious, especially in the lowlands of Pennsylvania, 
Maryland and West Virginia. They make mud piles which clog 
harvesting machines, and are considered by the farmers of Maryland 
as such pests that it is common to throw unslacked lime over the 
fields in order to kill the unwelcome tenants. West Virginia farmers 
claim that the crayfish destroys crops of buckwheat, corn and beans 
by eating the young sprouts. Great damage is done by the bur- 
rowing species, Cambarus diogenes, in burrowing into dams on ponds 
and reservoirs, a notable instance being the levees of the Mississippi. 

To destroy crayfish it is customary to throw unslacked lime over 
the field, or to pour carbon bisulphide into the holes, or to drain the 
infested area. None of these measures is efficacious, the first two 
methods being impracticable on account of the difficulty in reaching 
the bottom of the burrow and the last, simply lowering the water 
level, only delays matters a little. 

Economic Gain from Crayfish. — With the lobster fishery in a 
state of decline, it seems as if the crayfish could be profitably sub- 
stituted for its larger cousin. Crayfish mature in one season and 
grow to a length of from four to five inches in three years, so that, 
considering the large number of eggs (100-600) laid by one female, 
there should be but little difficulty in supplying a large demand for 
these animals. When we consider that the large Astacus readily 
adapts itself to the slight difference in environment in the east, we 
see that the crayfish is a very practicable substitute for the lobster. 
There should be no difficulty in disposing of the smaller Cambarus^ 
either as fresh food or canned, as we get the abdomens of shrimps. 

In school and college laboratories, the anatomy of the crayfish 
has been studied ever since Huxley wrote " The Crayfish." The 
habits and activities of the young and adult crayfish are of great 
interest and profit for study. The animal is suited for many kinds 
of experiments, and the large ganglia and nerve cells are readily 
removed and are excellent for neurological work. Psychologists 



lyo ARTHROPOD A 

should study the relations of mother and offspring for the few days 
just after the young are detached from the mother's swimmerets. 

References on the Crayfish and the Lobster 

Chidester, F. E. 191 2. The biology of the crayfish. Amer. Nat., vol. 

46, pp. 279-293. 
Herrick, F. H. 1911(1909). Natural History of the American Lobster. 

Bull. Bur. of Fish., vol. 29, pp. 149-408. 
Huxley, T. H. 1880. The Crayfish. D. Appleton Co. 

Crustacea. (Entomostraca and Malacostraca.) — The Branchio- 
poda, Ostracoda, Copepoda, and Cirripedia are certain Subclasses of 
primitively developed Crustacea which are grouped under the 
heading of Entomostraca as distinguished from the Malacostraca. 
They are small in size and while not themselves especially significant 
to man, they are of tremendous importance as the food of fishes. 

Subclass Branchiopoda. — These Crustacea generally have a shell, 
and many pairs of leaflike swimming appendages. The Order 
Phyllopoda includes the fairy shrimp and the brine shrimp. The 
fairy shrhnp, Branchipus^ a most beautiful form, is found in fresh 
water just after the ice has left certain ponds. The brine shrimps 
Artemia salina, has been the subject of experimental work on the 
influence of reduced and increased salinity on its characteristics. 
One species, Artemia jertilis^ is found in the Great Salt Lake. 

To the Order Cladocera ^ belong certain species of Daphnia. 
This form has a bivalved carapace enclosing the trunk. The eyes 
are sessile and fused. The interesting study of phagocytosis made 
by Metchnikoff showed that when the spores of a fungus, Mono- 
spora, were swallowed by Daphnia^ they perforated the wall of its 
alimentary canal, but were attacked and destroyed by the blood 
corpuscles. (Figure 75, A and B.) Elton reports a huge multipli- 
cation of water fleas in the Antwerp reservoirs in 1896 such that six 
men worked night and day removing them by straining the water 
through wire gauze. It was estimated that ten tons of water fleas 
were taken out. 

Subclass Ostracoda. — The common bivalved form Cypris uses 
Its antennae in swimming. It has no special economic significance, 
except as food for other animals. 

' Banta, A. M., and associates, have made numerous important studies on sex 
intergrades and the determination of sex in Cladocera. See his recent paper, Control 
of sex in Cladocera, Phys. Zool., vol. 2, Jan. 1929. 



ARTHROPODA 



171 



Subclass Copepoda. — These Entomostraca have no shell and 
lack abdominal appendages. They are among the most important 
fish foods. Forms like Cyclops are the best known. The parasitic 
guinea worm (page 96) is transmitted by Cyclops. The Copepoda 



Brood chamber 
Heart- 



Abdom. 



Abdominal 



Abdo. 




Mandible 
Anienna 



Anal 



Hepatic caeca 

|— Compound eye 
~ Ocellus 
^Antennule 

Labrum 



Fig. 75^^. Female Daphnia pulex, bearing summer eggs. 

Studies, vol. 11, 191 5.) 



(Dodds, Univ. of Colorado 



include many important fish parasites, the form Argulus being 
parasitic on the carp. Dr. C. B. Wilson of the U. S. Bureau of 
Fisheries is our international authority on parasitic Copepoda. 
(Figure 76.) Lake Plankton is rich in the Copepod Diaptomus. 

Frontal or nan 




Uferus 



/ 
/ 

' ^Median eye 
'^ .-/st. antenna 
^Paired eyes 

^Znd. antenna 



Caudal stylets' 

Fig. 755. Branchinecta packardii female showing uterus and eggs. (Dodds, Univ. 

of Colorado Studies, vol. 11, 191 5.) 

A number of species of Cyclops, colorless and blind, have been 
found in wells. 

SublcassCirripedia. — The Cirripedia (Figure 77) include the com- 
mon ^00 j-^w^-f/^ barnacle, Lepas, and the acorn barnacle, Balanus. The 
latter are found along the coast attached to rocks and wharves where 



172 



ARTHROPODA 





Fig. 77. Stalked barnacles {Lepas anatifera). 
(From Kellogg & Doane. Courtesy of Henry 
Holt & Co.) 




Fig. 76. Caligiis mutabilisy dor- 
sal view. F.P., frontal plates; 
C.A., cephalic area; L.A., lateral 
areas; T.A., thoracic area; F.S., 
free thoracic segment;G. 3"., genital 
segment; A., abdomen; E.S., egg 
strings. (Courtesy of C. B. 
Wilson.) 



Fig. 78. Sacculina, a crustacean parasite of 
crabs, {a) Attached to a crab, with root-like 
processes penetrating the crab's body; {b) re- 
moved from the crab. (From Jordan and 
Kellogg, Animal Life. Courtesy of D. Appleton 
&Co.) 



ARTHROPOD A 173 

their sharp shells are sources of much annoyance to bathers. Bar- 
nacles encrust the bottoms of ships. ^ Huxley described the barnacle 
as a " crustacean fixed by its head and kicking food into its mouth 
with its legs." One of the Cin-ipedia, a parasitic form known as 
Sacculina, is considered to be the most degenerate of parasites. 
(Figure 78.) It attacks the abdomen of crabs and causes degenera- 
tion of the gonads. Barnacles are degenerate crustaceans.^ The 
animals have lost their independence by attachment of the head or 
back, and the readjustment of segmental plates to suit the new 
needs. Embryology of the barnacles shows that they probably 
arose from free swimming phyllopods. Ruedemann discovered a 
primitive Balanus attached to the shell of a Cephalopod in the 
Ordovician shale, which also bears out this hypothesis. The goose- 
barnacles {Lepas) became fixed by the head, and developed several 
valves. 

Subclass Malacostraca. — The Malacostraca are usually large 
Crustacea, with five cephalic, eight thoracic and six abdominal 
segments, and with a grinding " gastric mill " in the stomach. 
The Malacostraca include lobsters, crabs, prawns, shrimps and pill 
bugs. The orders which we shall consider are the Amphipoda, the 
Isopoda and the Decapoda. The Amphipoda lack a carapace and 
have an elongated abdomen with three pairs of posteriorly directed 
feet, and three pairs of anteriorly directed swimming feet. 

The beach fleas ^ Amphipoda^ found on sea beaches, are important 
food for other marine animals. A boring amphipod, Chelura, 
attacks piles and wooden ships. The Isopoda have no carapace, a 
broad flat body, leaflike legs, and seven free thoracic segments. 
The wood-lice or sow bugs are Isopoda which live a wholly terrestrial 
life. They feed on decaying vegetable matter but sometimes 
damage plants in gardens and greenhouses. As they breathe by 
abdominal gills, they seek moist places. Some of their relatives 
live in fresh and salt water.'* 

^ Visscher, J. P. 1927. Nature and Extent of Fouling of Ships' Bottoms. Bull. 
U. S. Bur. Fish., vol. 43, 1927, Doc. 1031. Visscher found that paint of lighter colors 
should be used to prevent fouling of ships' bottoms while they are in port. Barnacles 
are stimulated most by light in the field of green and blue. 

^ Clarke, J. M. 1921. Organic Dependence and Disease. N. Y. State Museum. 

* Allee, W. C, who for over fifteen years has been studying animal aggregations in 
Isopoda and other forms, has recently given an excellent summary, Animal aggrega- 
tions, Qu. Rev. of Biol., 1927, vol. 1, no. 3, pp. 367-398. Consult also his book, Animal 
Aggregations, U. of Chi, Press, 1931. 



174 



ARTHROPODA 



An important genus, Lunnoria^ is found attacking submerged 
wood, sometimes honeycombing piles more than half an inch. Piles 
are accordingly creosoted or infiltrated with paraffin. (Figure 79.) 

The order Decapoda includes our common crabs, shrimps and 
lobsters. The first three pairs of thoracic appendages are modified 
as maxillipeds, the thoracic segments are covered by a carapace 
and there are five pairs of thoracic walking legs. The compound 
eyes are stalked. 




Fig. 79. Limnoria. (Courtesy of C. A. Kofoid.) 

There are two distinct genera oi crayfishes in America, Cambarus, 
found east of the Rocky Mountains, and Astacus extending to the 
Pacific coast. The latter genus includes individuals that grow to 
a length of 9 inches. The largest crayfish in the world, Astacopsis 
franklinii, found on the northwest coast of Tasmania, may weigh 
as much as 9 lbs. 

The American lobster, Homarus americanus, the European lob- 
ster, H. grammarus, and the Norwegian lobster, Nephrops nor- 
wegicus, are extremely important as food of fishermen and when 
served as delicacies inland. The lobster is found along the Atlantic 
coast, ranging from North Carolina to Labrador. The largest 
lobster ever taken weighed 34 lbs. and was 23.75 if^ches in length 
(Herrick). 



ARTHROPODA 175 

The sea crayfishes, Palinurus vulgaris, sometimes called the spiny 
or " rock lobsters," have no chelae and a much reduced rostrum. 
They are valued by Europeans for food and are said to be similar to 
the true lobster in flavor. The common prawn, Palaemonetes 
vulgaris, reaches a length of about 1 inches. It is transparent. 
The body is compressed and the exoskeleton lacks lime. The ros- 
trum, eye stalks and antennae are very conspicuous. The common 
shrimp, Crangon (Crago) vulgaris, is exceedingly abundant on the 
Pacific coast, along the shore of the Gulf of Mexico, The edible 
shrimp, Penaeus setijerus is found in shallow bays and estuaries 
from Virginia to Texas. It reaches a length of 6 inches. Its value 
as food is estimated to be over ^200,000 annually. While speaking 
of shrimps, we might mention the order Stomatopoda which includes 
Malacostraca with five pairs of anterior thoracic maxillipeds, three 
pairs of thoracic legs and an extremely short carapace. The 
mantis shrimp, Squilla {Chloridella) empusa, belonging to this order, 
reaches a length of 10 inches. Several species of Squilla are eaten 
in the Mediterranean and tropical Pacific. They are esteemed as 
a delicacy in Tahiti and Samoa. Perhaps the American form may 
yet come into use. 

The hermit crabs, Eupagurus, related to the shrimps and prawns, 
live in the shells of gastropods which they seek out very early in their 
life history and in which they are protected. Sea-anemones and 
hydroids are commonly found attached to the shells occupied by 
hermit crabs. (See Commensalism, p. 482.) Robber crabs {Birgus 
latro) are related land forms found on coral islands in the Indian 
Ocean, They ascend cocoanut trees, and feed on the pulp of the 
cocoanut. The blue crab {Callinectes hastatus) is the commercial 
soft-shell crab. Rock crabs and painted crabs are also used for food 
when soft. Oyster crabs bring a high price in the market. The 
ghost crab, a scavenger, destroys the eggs of sea birds. (Figure 80.) 
A little marina crab, Melia, inhabiting coral reefs, uses small sea- 
anemones for defense and for feeding. It captures an anemone 
in each claw and when attacked it thrusts the anemone towards 
the enemy for defense. When the anemones capture food, the crab 
seizes the tidbit. 

Class 2. Onychophora. — The Onychophora (Gr. onux, a claw; 
phoreo, bear) include approximately fifty species of the genus 
Peripatus, found in Australia, New Zealand, Africa, South America, 
and the West Indies. All the species of Peripatus are terrestrial, 



176 



ARTHROPODA 



living in damp places. About thirty species live In the tropics, 
eight appearing in Africa. Peripatus lives in crevices in rocks and 
other dark sheltered places, and moves slowly, avoiding strong light. 
It ejects slime from a pair of oral glands, capturing insects and 
Crustacea. Much as it resembles the hypothetical " ancestral 
Arthropod " of some zoologists, Peripatus is not ancestral, but merely 




Fig. 80. Above, male spider crab. Left, female spider crab. Right, ghost crab. 
Center, mud crab. (From Mayer, Seashore Life. Courtesy of N. Y. Zool. Soc.) 



a primitive type, modified from an old stock. When first discovered, 
it was termed a slug. Although it is an Arthropod, we find that 
Peripatus has a number of characteristics of the Annelida, such as 
paired segmental nephridia, and ciliated cells in the lining of the 
reproductive tubes. Like the Arthropoda, its appendages are 
modified as jaws, and it has well-developed tracheae, but lacks a 
coelom around the alimentary canal. (Figure 81.) 



ARTHROPODA 



177 



Class 3. Myriapoda. — The Myriafoda (Gr. murics^ ten thou- 
sand; podes, feet) have a head with paired antennae and mandibles, 
many similar body segments bearing leglike appendages, tracheae, 
and excretory (Malpighian) tubules which open into the intestine. 
The Millipeds are wormlike in appearance with about three hundred 
segments, to each of which is attached two pairs of appendages. 




Fig. 8 1 . Peripatus. (From Pearse, General Zoology. Courtesy of Henry Holt & Co.) 

Very few of them are injurious to agriculture. Julus is a crop 
destroyer. Centipedes have but one pair of appendages for each 
segment. The large tropical centipedes {Scolopendra) are reported 
to be extremely venomous and their bite may even be fatal to man. 
They reach a length of eighteen inches, are carnivorous and able to 
kill insects almost instantly. South American Indians use them as 
food. The house centipede {Scutigera forceps) feeds on flies, cock- 
roaches, and bed-bugs and since it is not very poisonous to man, is 
of considerable economic importance. 

Class 4. Hexapoda. (Insecta.) (Gr. hex., six; ?Ln6.pous, foot.) 
— We live in the Age of Insects, and struggle with them for the 
possession of the earth. Not only physical and chemical agencies, 
but all available natural enemies must be utilized in order to keep 
the insects under control. They devour our foodstuffs, destroy our 
animal friends and still prevent us from claiming important new 
territory. The number of species of insects outnumbers those of 
all other animals taken together, and the number of individuals is 
incalculable. Little is known about the histology, embryology or 
physiology of insects, but all that we do know has shown that they 
are of tremendous importance economically. Interesting studies 
of their habits have shown that insects are highly developed and 
specialized in their behavior. 

The Insecta have three well-defined regions, the head, thorax and 



Wings membranous 

Fore wings parchment-like. 



178 ARTHROPODA 

abdomen. All insects have three pairs of thoracic legs and the 
majority have one or two pairs of thoracic wings. Respiration is 
accomplished by means of a complicated tracheal system. Insect 
classification is based on the structure of the mouth parts and the 
character of the development. Aldrich reported (1907) that there 
were 640,000 named insect species. 

Classification ^ 

Metamorphosis very slight; biting mouth parts; wingless Thysanura. 

Metamorphosis incomplete. 

With biting mouth parts. 

Ephemerida. 

Plecoptera. 

Odonata. 

Isoptera. 

Corrodentia. 

fOrthoptera. 

Euplexoptera. 

Wingless Mallophaga. 

\nT II- 1 J Hemiptera. 

W ith suckmg mouth parts < „, ^ 

"^ ^ 1 hysanoptera. 

Metamorphosis complete. 

With biting mouth parts. 

Neuroptera. 

With wings membranous s Mecoptera. 

Trichoptera. 

With fore wings thickened Coleoptera. 

H7- LI- 1 J Lepidoptera. 

With suckmg mouth parts S t^- 

^ ^ IDiptera. 

With lapping or piercing and sucking mouth parts < „ 

Folsom (1922) gives a most elaborate classification of insects 
according to food habits: Microphaga, feeders on sugars and salts, 
with yeasts and bacteria; sarcophaga, flesh eaters; copraphaga, 
eaters of molds and bacteria; mycetophaga, consumers of fungi; 
necrophaga, eaters of dead animals, etc. (A flesh-eating insect 
larva may eat 200 times its own weight in 24 hours.) In America 
it is customary to classify the insects into 19 orders. We will 
consider them thus, treating briefly of each order. 

Insects. Order 1. Thysanura. {Aptera). — T\vt Thysanura \n- 
clude wingless insects with retracted mouth parts and no meta- 

^ Classification after Kellogg and Doane. 



ARTHROPODA 



179 



morphosis. The common ''fish moth " or stive}' fish attacks starched 
clothing, book bindings and wall paper paste, and the " snow flea " 
sometimes gets into maple sap. 

Order 2. Ephemerida. — The May-flies have delicate wings, 
poorly developed mouth parts and an incomplete metamorphosis. 
The young May-fly lives in the water. Adult May-flies are said to 
take no food, but to mate, deposit their eggs and die, all within the 
short span of twenty-four hours. (Figure 82.) 




«rt 



Fig. 82. Young nymph of May-fly, showing tracheal gills. (After Jenkins and 
Kellogg, from Kellogg and Doane, Zoology and Entomology. Courtesy of Henry Holt 
& Co.) 



Order 3. Odonata. — The dragon flies, as larvae and as adults, 
are important enemies of mosquitoes. They have large compound 
eyes, four membranous wings and strong, biting mouth parts. 

Order 4. Plecoptera. — The stone flies are less important as fish 
food. The nymphs live in running water where they cling under 
stones. 

Order 5. Isoptera. — The termites or " white ants " are found in 
the tropics in great abundance, where they destroy houses and other 
structures made of wood. Some species attack soft plants and living 
trees. In Africa, they sometimes build pyramidal nests twenty feet 
high. The termites are social insects. (See p. 484.) 

Order 6. Corrodentia. — The book-lice are wingless insects 
frequently found defacing the paper and bindings of old books. 
Bark lice are winged forms feeding on lichens, oak leaves and other 
foliage. 

Order 7. Mallophaga. — There are about fifteen hundred species 
of biting lice which live among the feathers of birds or the hair of 
mammals. While they are not sucking forms, they cause bleeding 
and the results are almost as bad. They irritate the animals which 
resort to dust baths. 



i8o ARTHROPODA 

Order 8. Thysanoptera. — The thrips are minor pests of wheat, 
onions, citrus fruits and grasses. Their feet are clawless with blad- 
ders adapted for clinging to leaves. They have four narrow mem- 
branous wings, fringed with long hairs. 

Order 9. Euplexoptera. — The earwigs feed on fruit and flowers, 
but are of no economic significance in America, where they are 
rare. The mother remains to guard her eggs for a time. 

Order 10. Orthoptera. — The cockroaches, Blattidae, are noc- 
turnal insects frequenting water pipes and attacking food stuffs. 
There are four species in the U. S., the common " croton bug " being 
the form most frequently found. They eat the " silver-fish," bed- 
bugs and each other. 

The praying mantis, Mantidae, has its front legs peculiarly 
adapted for seizing and holding its prey. Its peculiar attitude when 
lying in wait for its food gives it the name " praying." 

The walking sticks, Phasmidae, resemble their background so 
perfectly that it is exceedingly difficult to locate them at times. 
They feed on the leaves of trees, usually the oak. 

Locusts or short-horned grasshoppers, Acrididae, have extremely 
short antennae and well-developed leaping legs. They are impor- 
tant enemies of plant life and, when they migrate in hordes, seem to 
devour almost everything. Locusts were eaten in the Orient and 
are still prized by some savages. (Figure 83.) 

The Tettigoniidae {Locustidae) include the meadow grasshoppers 
and the katydids. The katydids are large green insects feeding on 
leaves and tender shoots, but occasionally devouring other insects. 
'Y\\t females are silent. Certain yellowish brown, wingless forms, 
living in cellars and caves, are called " cave crickets." 

The Gryllidae have their wings flat on the body and are usually 
stout-bodied. Many are wingless. The true crickets (house 
crickets) are black forms, feeding on plants for the most part. 
The eggs are laid in the ground in the fall and hatch in the summer. 
The tree crickets are slender and light in color. The " snowy tree 
cricket " injures grape vines and berry plants. The female guards 
her eggs. The mole cricket has its front tibiae broadened for bur- 
rowing. It is an important enemy of growing plants, particularly 
the potato. 

Type of the Order — Lubber Grasshopper — Rhomaleum Microp- 
ierum. Anatomy. — The grasshopper is divided into three distinct 
regions: The head, the thorax with three segments, and the abdo- 



ARTHROPODA 



i8i 



men consisting of eleven segments. The head is rather elongated 
dorsiventrally and bears two rather large laterally situated com- 
pound eyes with many facets. There are three simple eyes, the 
ocelli, one near the middle of the forehead and the others situated 
near the bases of the antennae. The antennae are long and seg- 
mented to give flexibility. They bear many spines which furnish 
increased points of contact. The mouth parts consist of a dorsally 
situated labrum; two crushing mandibles with serrated edges; a 
pair of maxillae, each provided with a maxillary palp; and a ventral 
labium with a pair of labial palps. 



antennae 




•ovipositor 



fern uri 
tibia'' 

tarsal segments 



Fig. 83. Locust, with external parts named. (From Kellogg, The Animals and Man. 

Courtesy of Henry Holt & Co.) 



The thorax consists of three segments, prothorax, mesothorax and 
metathorax, with a pair of legs attached to each of the segments. 
The third and second thoracic segments bear wings in the grass- 
hoppers. The anterior pair of wings are wing covers and used for 
gliding, while the posterior pair, folded like a fan when at rest, are 
the true flying wings. 

The abdomen consists of eleven segments. In the male there are 
nine distinct movable sterna. The posterior end in the female is 
modified by hardened ovipositors, the tips of which are protruded 
beyond the eleventh tergum. During oviposition, the tips are 



l82 



ARTHROPODA 




ARTHROPODA 183 

forced into the ground, then separated, forming a pit for the reception 
of the eggs. 

The Digestive System. — From the anterior mouth a short rather 
broad esophagus (Fig. 84) extends dorsally and posteriorly into the 
thorax, where it enlarges to form a thick-walled a-op or ingluvies, 
which extends through the mesothoracic and metathoracic segments. 

On each side of the anterior end of the crop are delicate branched 
salivary glands which communicate by means of salivary ducts with 
the mouth cavity. The proventriculus is not constricted from the 
crop, but extends a short distance to the stomach. The stomach 
or ventriculus extends to the seventh abdominal segment. At the 
point where the ventriculus originates, there are eight cylindrical 
pouches, the gastric cecat, extending anteriorly on the sides of the 
proventriculus and continuing as eight diverticula or c&c?if^ posteriorly 
along the sides of the ventriculus. No liver is present. The ileum^ 
or intestine which has noticeably hardened walls, is found in the 
seventh, eighth and ninth abdominal segments, constricting poste- 
riorly as it enters the colon or hind intestine, which runs dorsally 
down the ninth and tenth segments. The rectum is a small white 
enlargement situated in the dorsal portions of the ninth and tenth 
segments and emptying at the anus on the lower surface of the 
eleventh tergum. 

Respiratory System. — In the grasshopper there are two pairs of 
thoracic stigmata or spiracles. Eight pairs of abdominal spiracles 
are situated laterally just above the pleurons, the most conspicuous 
being the pair found on the anterior margins of the tympani. Ex- 
tending throughout the body, we find a well-developed system of 
tracheal tubes, which take the place of the complicated circulatory 
system found in some other invertebrates, but lacking in the Arthro- 
poda. 

Circulatory System. — The heart is a long, narrow vessel, extend- 
ing in the dorsal portion of the abdomen. It is divided by valves 
into chambers, the anterior one being called the aorta. There are 
no arteries or veins, but the blood passes through sinuses and finally 
enters the heart through lateral ostia. (Many of the strongest 
cardiac poisons have no action whatever on the insects.) 

Urinary System. — The Malpighian tubules are masses of fine 
tubes, anterior to the rectum, and open into the intestine. They 
are primitive kidneys. 

Reproductive System. — The ovaries consist of a long white struc- 



1 84 ARTHROPOD A 

ture above the ventriculus and intestine made up of two sets of tubes 
bound together into a compact mass. Two delicate oviducts pass 
posteriorly around the ileum and colon to the ventral portion of the 
body where they unite to form the single median vagina which opens 
on the upper surface of the subgenital plate at the ovipositor. The 
spermatheca is a small white pouch situated above the posterior end 
of the vagina and communicating with it at the bursa copulatrix 
by means of a minute orifice. The testes consist of two sets of 
coiled tubules bound together in one mass and situated above the 
intestine. Each testis sends off a vas deferens, the two uniting to 
form a median ejaculatory duct. To each vas deferens is attached a 
seminal vesicle, while cement glands empty into the ejaculatory duct. 

The Nervous System consists of dorsally situated cerebral ganglia, 
two circum-esophageal connectives, a pair o{ fused sub-esophageal, 
three pairs of fused thoracic, and five pairs of fused abdoyninal 
ganglia. The thoracic ganglia are much larger than those of the 
abdomen. Such highly developed concentration of ganglia in 
cephalic and thoracic regions indicates a very high development of 
reactions. In the ants and bees we find even greater concentration. 

Order 11. Hemiptera. — The Hejniptera have sucking mouth 
parts and when wings are present, they have four. Most of the 
Hemiptera are winged. Some generations of aphids are wingless. 

The Heteroptera, true bugs, include aquatic and land forms. 
The giant water bugs (Belostomatidae) are important enemies of 
insects, tadpoles and small fishes. The harlequin cabbage bug is an 
important pest in the South, while the gj-een soldier bug and the 
spined soldier bug are predaceous, destroying the larvae of injurious 
Hexapoda. The squash bugs {Coreidae) and allied forms attack 
squashes, pumpkins and other garden vegetables. The assassin 
bugs {Reduviidae) are predaceous forms attacking other insects 
such as the bed-bug. They may even attack man. The Indian 
bed-bug {Cimex hemipterus) and the common bed-bug {Cimex lec- 
tularius) transmit dum-dum fever, a flagellate disease. (See p. 29.) 
The chinch-bug is one of the worst pests of corn known and also 
attacks wheat. The leaf bugs attack foliage. 

The most important of the Homoptera are the scale insects and 
the plant lice. The cicadas {Cicadidae) include a form known as the 
seventeen-year " locust," which lives underground as a nymph from 
thirteen to seventeen years. The eggs are laid in living twigs. 
They hatch in about six weeks, burrow into the ground and feed on 



ARTHROPOD A 185 

the juices of roots until the seventeenth year, when they emerge, 
moult and become adults. 

The plant lice or aphids {Aphididae) Include our most destructive 
greenhouse and orchard pests. The grape phylloxeran {Phylloxera 
vastatrix) causes decay of the roots of grapevines. Aphids undergo 
parthenogenetic development. (See p. 123.) 

The scale insects, especially the San Jose scale, are extremely 
injurious to fruits. The cottony-cushion-scale, which attacks the 
orange groves of California, was successfully controlled by the lady 
beetle ( Novius cardittalis) Imported from Australia. 

Several families of plant hoppers occur. These Include the 
spittle Insects, the lantern flies, some of which are luminescent, the 
leaf hoppers and the tree hoppers. The leaf hoppers are injurious 
and difficult to control. 

Certain Hemiptera, known as the Parasitica {Anoplura), are 
wingless and constitute formidable enemies of man and other mam- 
mals. The species that Infest man (Genus — Pediculus) Include the 
head louse, the body louse and the crab louse. Domestic animals are 
infested by the genus Haematopinus. 

Order 12. Neuroptera. — A number of orders were formerly 
grouped under the Neuroptera, but are now separated. The order 
Neuroptera includes some very large Insects. They have four long 
narrow and finely netted wings. Their metamorphosis is complete 
and they have biting mouth parts. Their antennae are conspicuous. 

Larvae of the dobsonfly, known as " helgrammltes," are used for 
fish bait. The a7it lions, or " doodle-bugs," make pits in sand, dust 
or decayed wood, capturing thus many small insects. The adult 
ant lion resembles a damsel fly. 

The lace-winged flies or " aphis lions" have thin lacy wings and 
are green in color. Their larvae resemble those of the ant lions 
but have yellow or red markings. They feed on colonies of plant 
lice. The adults have brilliant golden eyes. 

Order 13. Mecoptera. — The scorpion flies have four membra- 
nous wings, thickly veined but with few cross-veins. The head is 
beaked and the mouth parts are adapted for biting. Metamorphosis 
Is complete. Scorpion flies feed on small insects. Both the larvae 
and the adults are carnivorous. 

Order 14. Trichoptera.—The caddice flies have rudimentary 
mouth parts, four membranous wings thinly clothed with hairs, and 
have complete metamorphosis. The aquatic larvae lack pro-legs 




1 86 ARTHROPODA 

and form cocoons of sand, pebbles and silk, which are easily recog- 
nized as those of the " caddice-worm." 

Order 15. Lepidoptera. — Lepidoptera have four wings covered 
with fine, powdery scales. The larvae of moths and butterflies, 

called caterpillars, are 
worm-like, having three 
pairs of true thoracic legs 
and from one to five pairs 
of pro-legs. 

„ . ^. ., . Micro - Lepidoptera in- 

FiG. 85. Case or Discosmoecus gilvtpes. , , , ^ ... 

(Dodds, G. S., and Hisaw, F. L., Ecology, ^^^^^ /^e super-families 
vol. 6, no. 2.) Pyralidina, Tortricina and 

Tineina. 

The Pyralidina or " leaf-rollers " feed on stored grain. The 
European corn borer {Pyrausta nubilalis), an important pest in this 
country, appears to accumulate in destructive numbers in areas of 
naturally high soil and atmospheric moisture. Meal moth {Pyralis 
farinalis) larvae feed on meal and flour, making tubes of silk in the 
77teal. The Mediterranean flour moth {Ephestia kushniella) is one of 
the most injurious forms, infesting flour mills. Other injurious 
forms are the meal-moth, the clover-hay worm, the melon-worm and 
the pickle-worm. The Tineina^ smallest of the Lepidoptera, include 
the grain moths and the clothes moths. Grain moths attack grains 
both in the field and stored. The common clothes moths are yellowish 
moths whose larvae do a great deal of damage to woolen clothing 
and furs. (Figure 86, A and 5.) 

The family Tortricina includes the bud moth which attacks young 
shoots of apple trees, the strawberry leaf roller and the extremely 
injurious codling moth. The codling moth causes an annual loss of 
over ^12,000,000. The larvae burrow through the blossom end of 
an apple and eat their way to the core, devouring the seeds. The 
larvae of the second generation usually feed on the surface of the 
apple. In the fall the larvae burrow into crevices of the bark, spin 
white silk cocoons and hibernate. The Oriental fruit worm was 
introduced on the ornamental cherry trees sent from Japan to 
decorate the city of Washington, It attacks twigs and young 
peaches. The Noctuidae are the largest family in the order, with 
more destructive forms than any other. The army worms migrate 
from field to field in large bodies. The corn ear worm or cotton-boll 
worm, the cotton worm^ and the cabbage looper are a few of the more 



ARTHROPOD A 187 

important pests. The cotton-boll worm and the cotton worm cause 
millions of dollars loss annually to the cotton growers. The 
Bombycidae include the coinmon silk-worm moth. The silk worm has 
been artificially bred in China for over five thousand years. 

Some of the largest and most showy of the moths belong to the 
giant silk worm family, the Saturniidae. These include the Poly- 
phemus, the Cecropia, and the Luna moths. The Cecropias are a 
trifle injurious to shade trees, but in general these species are 
interesting only on account of their size. The carpenter moths 
(Cossidae) are wood-borers attacking trees. 





A B 

Fig. 86. yf, clothes moth. 5, larva of clothes moth. (After Riley. U. S. Dept. Agr.) 

The Geometridae are called " measuring worms " when in the 
larval state. An extremely important species is the spring canker 
worm (Paleacrita vernata) whose larvae feed on the leaves of fruit 
trees. The Liparidae or tussock moths injure shade trees. The 
white marked tussock moth is a native form injurious to fruit and 
shade trees, while the antique or rusty tussock moth is a European 
species found in Nova Scotia, New England and the West. The 
brown tail moth attacks shade and forest trees, but avoids the 
conifers. The gypsy moth has spread from the New England states 
into some of the Middle Atlantic states. The Sphingidae include 
the hawk moths or humming bird moths. They have long tongues 
adapted for sucking nectar from flowers like honeysuckles. The 
butterflies have their antennae enlarged at the tips, and fly exclu- 
sively in the daytime^ while moths fly at night and have threadlike 
or feathery antennae. There are two great super-families, the 
Papilionina or true butterflies and the Hesperina or skippers. 

The Nymphalidae include forms with poorly developed front 
legs, not adapted to walking. Some of the more common forms are 
the thistle butterfly, the Admiral, the wood nymph and the viceroy. 
The viceroy is interesting because it closely resembles the bad tasting 



1 88 ARTHROPODA 

monarch butterfly and is supposed to be thus protected. (Natural 
Selection, p. 515.) The swallow-tailed butterflies (Papilionidae) 
include the black swallow tail whose larvae feed on celery and parsley; 
and the tiger swallow tail^ yellow in color, which is the largest common 
species. Caterpillars of the cabbage butterflies devour the outer 
leaves, then bore to the heart of the cabbage. 

The alfalfa caterpillar {Ewymus) attacks alfalfa in the West. 
The gossamer winged butterflies {Lycaenidae) are the smallest and 
most delicate butterflies. The larvae are small and slug-like and 
feed on plants. One carnivorous form, the " harvester," is valuable 
to the fruit-grower since its larva feeds on the wooly aphids. 

Pigment in Butterfly Wings. — One of the present day fads is that 
of enclosing butterfly wings in glass brooches. The natural color 
should remain for some time since colors in the wings of fossil but- 
terflies were found persistent when exhumed by Dr. R. J. Tillyard 
millions of years after they were sealed with mud. Exposure to the 
air caused rapid fading, however. 

Order 16. Diptera. {Flies, Mosquitos, etc.) — The Diptera, as 
the name indicates, have two wings. They have sucking mouth 
parts, and the metamorphosis is complete. There are over 7,000 
species of Diptera in North America. 

The common housefly {Musca domesticd) carries typhoid, tubercu- 
losis and other bacterial diseases. It is also important in the 
transmission of the eggs of several species of Nematode and Cestode 
worms. A fly wing is said to vibrate 330 times per second. House- 
flies lap up liquid food with their folding proboscis. 

The blow fly and th.& flesh fly {Sarcophagidae) deposit their eggs 
on meat and cheese on which the maggots feed. The horse fly 
{Tabanidae) attacks cattle and horses and even man. The female 
feeds on blood, but the male lives on nectar. The tachina fly 
{Tachinidae) is an important enemy of caterpillars (particularly 
the army worm), and kills many locusts and leaf-eating beetles. 

The bot-flies {Oestridae) attack cattle and horses. The eggs of 
the horse bot-fly, licked off their legs by infested animals, develop 
in the lining of the stomach until the time of pupation when they 
are extruded. 

The ox-warble larvae ( Hypoderma lineata) pass to the esophagus 
of the host in the same manner as those of the horse bot-fly, but 
then burrow into the subcutaneous tissue and lodge just under the 



ARTHROPOD A 189 

skin where they cause lumps. Ultimately they develop and pass 
out through the hide, riddling it with holes. Herms cites a case of 
the ox warble in a child in which the grub, Hypoderma lineata^ 
travelled from below the knee to a point behind the ear, taking 
about two months' time. 

The sheep-bot flies, living in the nostrils of sheep and antelopes, 
travel up the frontal sinus and cause the disease known as " stag- 
gers." Other bot-flies attack rodents and even man. One form, 
Dermatobia hominis, found in Mexico, Central, and South America, 
attacks Birds, Mammals and Man. It is transported by certain 
mosquitoes, particularly Psorophora lutzi. The larval period re- 
quires about three months. 

Mosquitoes {Culicidae) ^ have slender sharp-pointed mandibles, 
enabling them to puncture the skin of animals. Mosquitoes are 
extremely important in the transmission of parasites causing disease. 
They include three important groups: Anopheles, Aedes, and Culex. 
(Figure 87.) 

In the Anopheliites, the head has upright forked scales and the 
palpi in both sexes are almost as long as the proboscis. Anopheles 
larvae lack a siphon tube and breathe through a stigmatic opening 
on the eighth abdominal segment. They rest at the surface 
of the water. In resting, as in the position of biting, the Anoph- 
eles adult elevates its body in a characteristic manner (Figure 88). 
Anopheles quadrimaculatus and several allied species transmit 
malaria. Bird malaria is transmitted by the Culicine mosquitoes 
{Culex pipieyts). 

In Aedes {Stegomyia) (Figure 89), the head has a few forked 
scales and a mass of flat scales covering the head while the palpi 
are less than one-half as long as the proboscis. Aedes larvae have a 
short, conical siphon tube, and hang down from the surface of the 
water. The successful completion of the Panama Canal was ac- 
complished only after measures were taken to kill the yellow fever 
transmitting mosquito, Aedes egyptii {Stegomyia calopus). 

In the Culicines, the head has a few flat scales, but many narrow 
curved and upright forked scales. The palpi of the male are nearly 

1 Varro, the Roman author, cautions the builder against placing his farm-house 
on swampy ground " because certain minute animals, invisible to the eye, breed there, 
and, borne by the air, reach the inside of the body by way of the mouth and nose and 
cause diseases which are difficult to get rid of." Centuries later mosquitoes were 
proved to be the carriers of malaria and yellow fever. 



190 



ARTHROPODA 







Anopheles. Female Anopheles, Male Culex, Female Culex 

A 




Fig. 87. A, structural characteristics of antennae of Culex and Anopheles. B, 
resting position of Culex mosquito (above), and Anopheles mosquito. (Courtesy of 
Major George C. Dunham, and U. S. Army Medical Field Service School.) 



ARTHROPODA 



191 



as long as the proboscis, while those of the female are less than one- 
half as long. Culex larvae have a slender, long siphon, and hang 
down from the surface of the water. The adults in resting position 
do not elevate the abdomen as in the Anophelines. Filariasis, the 
disease known as elephantiasis, which is caused by a small nematode, 




Fig. 88. Larvae of Anopheles, above, and Culex, below, in feeding and breathing 
position. (From Howard, Mosquitoes oj the U. S.) 

Microfilaria bancrofti, is transmitted through the agency of a Culi- 
cine mosquito, Culex {fatigans) quinquefasciatus. Dengue, or 
breakbone fever, is a tropical disease, found in Mexico, which is 
transmitted by both Culex fatigans and Stegornyia calopus. 

Poison. — The poison of female mosquitoes has not been thor- 
oughly studied, but Noguchi reports that there are three sets of 
glands, two of which are ordinary salivary glands, and the third set, 



192 



ARTHROPODA 




Fig. 89. Yellow-fever mosquito, Stegomyia fas- 
ciata. (Howard, F. B., 1354, U. S. D. A.) 



situated between the 
other two, secretes the 
poison. If a mosquito 
punctures the skin, but 
does not reach blood, 
the poison is not injected. 
An anticoagulant is pro- 
duced by the mosquito. 

The gall gnats {Ceci- 
dofnyiidae) are terrestrial 
forms attacking many- 
plants and producing 
" galls." The Hessian- 
fly, a small black form, 
is estimated to damage 
wheat and rye to the ex- 
tent of many millions of 
dollars annually. The 
crane flies ( Tipulidae) 
somewhat resemble mo- 
squitoes. They are often 
quite large, with long, 
loosely attached legs. 





Fig. 90. Male and female fruit flies {Drosophila melanogaster) . (Morgan, Physical 
Basis of Heredity. Courtesy of J. B. Lippincott Co.) 



ARTHROPODA 193 

Their larvae live in the soil and injure the roots of plants. The 
midges {Chironomidae) are small flies somewhat resembling mo- 
squitoes. In the larval state they are red, wormlike, aquatic forms. 
The black flies {Simuliidae) are aquatic in the larval state, and the 
adults are great pests in some localities since they are blood suckers 
and attack fishermen. 

T\\& fruit flies, particularly the Drosophilidae (Fig. 90), are used 
in investigations on heredity. (See p. 538.) There are about 
1,000 species of Trypaneidae attacking various fruits. The Mediter- 
ranean fruit fly ^ {Ceratitis capitata), known for over 100 years, and 
of considerable importance in the Mediterranean countries and 
more recently in Hawaii, was discovered in Florida on April 6, 1929. 
Its life cycle takes from 30 to 40 days, pupation occurring in the 
ground. In Hawaii and in South Africa, Ceratitis capitata has 
proven a serious pest of the citrus fruits, but also attacks deciduous 
fruits such as peaches and apricots. Lemons are practically im- 
mune to this pest, but sour oranges are more susceptible than the 
sweet varieties. In Hawaii, poison sprays have not been used with 
any degree of success, but they 
appear to be more effective in 
the U. S. 

The Syrphus flies {Syrphi- 
dae) are important enemies of 
the aphids and feed on nectar 
and pollen. Some are scaven- p^^ ^^ ^ "rat-tailed" larva (Syr- 
gers, the " rat-tailed " larvae phidae). (Smith, Insects of New Jersey, 
feeding on foul organic matter. N.J. Board of Agr.) 
(Figure 91.) 

Some of the species " mimic " the bees and wasps. According 
to the ancient Bugonia myth, bees develop in the carcasses of dead 
animals, but the drone-flies {Eristalis tenax) are the forms thus 
found. The reactions of the drone-fly to light have been extensively 
studied by Dolley.^ 

8 In climates where the mean temperature fails below 50° F. over periods covering 
3 months, there is little development of Ceratitis capitata and accordingly it is hoped 
that we can limit its ravages to the Southern states. (Herrick, G. W. The procession 
of foreign insect pests. Sc. Mon., vol. 29, pp. 269-274.) 

'W. L. Dolley, Jr., and J. L. Wierda. 1929. Relative sensitivity to light in 
different parts of the compound eye in Eristalis tenax. Jour. Exp. Zool., vol. 43, pp. 
129-139, May. 




194 



ARTHROPODA 



The sheep tick, the horse tick and various bird ticks belong to 
the sub-order Pupipara. 

Order 17. Siphonaptera. (Fleas.) — The Siphonaptera, or fleas, 
are wingless, with sucking mouth parts and complete metamorpho- 
sis. There are about 50 species in the United States. The common 
cat and dog flea, Ctenocephalus canis, attacks man. The human 
flea (Pulex irritans) and the chigoe or " chigger " {Sarcopsylla pene- 
trans) are important enemies of man, the latter burrowing into the 
skin. This is not the common chigger, which is a mite. (See page 
201.) 

The rat flea {Laemopsylla cheopus) transmits bubonic plague from 
rats and ground squirrels to man. Fleas may start out with one 
animal as a host and transfer to its enemy. 

Order 18. Coleoptera. (Beetles.) — The beetles have four 
wings, well-developed biting mouth parts, and a complete meta- 
morphosis. There are over 12,000 species found in America, ex- 
clusive of Mexico. 

The tiger beetles (Cicindelidae), both in the larval and adult 
states, are important enemies of insects and crustaceans. The 
larvae live in holes in the ground. The ground beetles (Carabidae) 
are extremely important predaceous insects. They destroy the 
larvae and adults of many injurious leaf-eating insects. The cater- 
pillar hunter (Calosoma scrutator) is an important enemy of the 
hairy " tent-caterpillar." Other forms attack cut-worms and 
canker worms. A few species feed on young grains, but the majority 
of the Carabidae are beneficial. The carnivorous water beetles 
(Dytiscidae), a.re important enemies of mosquitoes and other injurious 
insects. The larva, the ferocious " water-tiger " traps air under the 
hairs of its tergum and is able to remain under water for some time. 
Large " tigers " reach a length of three inches. The water scavengers 
(Hydrophilidae) are large forms living under the surface of water 
during the day, but flying to lights at night. They are black and 
over an inch in length. The whirligig beetles (Gyrinidae) are small 
aquatic forms not more than ^ of an inch long. Children some- 
times call them " money-bugs." The lady bugs (Coccinellidae) or 
" lady-bird beetles " are predaceous in the larval as well as the 
adult condition. They are important agents in the control of plant 
lice and scale insects. The genus Epilachne is herbivorous. 

The carpet beetle (Anthrenus scrophulariae) attacks rugs and 
clothing, including feathers. The club-horned beetles (Clavicornia) 



ARTHROPODA 195 

may be found on land and in the water. Some are herbivorous and 
exceedingly injurious. The Dermestidae destroy stored grains. 
The saw-toothed grain beetle {Cucujidae) is an extremely injurious 
species. 

The buffalo-moth attacks wool, feathers and furs, while the 
larder beetle destroys and spoils animal food products. The 
Elateridae, or click-beetles, are interesting as adults, but their larvae, 
called wire-worms, attack plants and seeds. Certain of the wood 
borers {Buprestidae) are distinguished as the flat-headed borers. 

T\iQ fireflies or Latnpyridae are luminous insects flying at night. 
Many non-luminous forms belong to the same family. The blade 
horned beetles or LaiJiellicornia have antennae with their terminal 
joints developed into leaflike plates forming a club. There are two 
families, the Lucanidae or stag-beetles, and the Scarabaeidae. One of 
the most familiar forms is the stag-beetle, with its long mandibles 
or " antlers." Some males have well-developed mandibles and are 
tailed " pinching bugs." The Scarabaeidae include the most of the 
Lamellicorns. The leaf chafers feed on flowers and leaves. The 
scavenger beetles bury or eat decaying matter. The sacred beetle 
or Scarab, found in Egyptian tombs, is a species of dung-feeding 
tumble bug. Egyptians worshipped the scarab because it killed 
worms. Other forms notably injurious are the 'June bug and the 
rose chafer. The larval June bug called the white grub or " molly 
grub " is of considerable injury to underground roots, while the 
adult form, injurious to foliage in a less degree, is a household 
annoyance in the early summer. The "Japanese beetle {Popillia 
japonica), a serious pest, was imported into New Jersey and Penn- 
sylvania and has spread into adjoining states at the rate of about 
twenty miles per year. The rhinoceros beetle is the largest American 
species. In the West Indies related forms reach a length of six 
inches. 

The plant eating beetles ( Phytophaga) include the pea and bean 
weevils {Bruchidae), the leaf beetles {Chrysomelidae), and the long- 
horned beetles {Cerambycidae). 

The Bruchidae larvae feed on the seeds of peas and beans and are 
called bean-weevils. The most injurious Chrysomelids include the 
elm-leaf beetle, and the Colorado potato beetle, which is one of the 
largest of the Chrysomelids and an important enemy of the potato. 
The Cerambycidae are long-horned beetles including many wood- 
boring forms, such as the apple tree borers and the maple borers. 



196 



ARTHROPODA 



The larvae are called the " round-headed borers " to distinguish 
them from the Buprestid larvae which are flat-headed. The 
Tenebrionidae include the ordinary meal worm which is a minor pest 
in spoiled grain, but is useful in feeding pet birds and " horned 
toads." The Meloidae, or blister beetles, feed on plants. They are 
used to supply the cantharides or Spanish fly used for blistering. 
The snout beetles {Rhynchophord) include the bark beetles, most 
destructive to trees, and the Curculios or weevils. The Mexican 
cotton-boll-weevil has cost the South many thousands of dollars by 
destroying its cotton, while the alfalfa weevil is a serious pest on the 
West Coast. 




Fig. 92. Blastophagay the insect which pollinates figs. (U. S. D. A.) 



Order 19. Hymenoptera. {Gall-flies, Ants, Wasps and Bees.) — 
The sawflies, horntails and gall flies are boring Hymenoptera whose 
larvae feed on the leaves of shrubs and in some cases induce develop- 
ment oi galls. 

The chalcid flies {Chalcidoidae), minute parasites attacking the 
eggs and larvae of injurious insects, are for the most part extremely 
beneficial to man. One species is responsible for the fertilization 
of the fig. The fig-wasp has recently been introduced from Asia 
Minor into California. The gall-flies {Cynipoidea) utilize a sharp 
ovipositor to thrust their eggs into green stems of oaks, roses and a 
few other plants where the hatching larvae stimulate the plant to 



ARTHROPOD A 197 

form a gall. The giant oak-gall grows to the size of the human fist. 

The Ichneumonoidae are parasitic hymenoptera attacking many- 
injurious insects such as the cabbage butterfly, tent-caterpillars, 
cotton-worms, brown-tail and tussock moths. 

The braconid flies {Braconidae) are also valuable in that they 
parasitize plant lice, tomato worms, sphinx caterpillars and fall 
web-worms. The Serphoidea are a group of mostly small insects 
parasitic on other insects. 

In the stinging hymenoptera, which include the ants, bees and 
wasps, the females and workers sometimes have the ovipositor 
developed into a " sting." 

Ants. {Fo7-micoidea.) — Found in nearly all parts of the world, 
and comprising some twenty-five hundred species, ants have de- 
veloped to a marked degree a differentiation in body structure and in 
habits. The first two segments of the abdomen are expanded dor- 
sally, serving as a peduncle to the rest of the abdomen. The nest 
or home, usually underground, is divided into many channels and 
passages. 

The carpenter ant {Camponotus penn) builds its nest in the dead 
wood of living trees and of buildings. The mound building a?jt 
builds ant hills ten feet in diameter. The slave making ants {Formica 
difficilis) depend on their servants (other ants) for shelter and food. 
(See Communities, p. 484.) 

The corn louse ant {Lasius brunneus) tenderly cares for one of the 
extremely injurious aphids attacking the roots of corn. The tiny 
red ant {Myrmicidae) , while something of a pest in this country, 
becomes an actual menace in the Orient. 

Stingless ants, the Campanothinae, are provided with a cushion- 
like poison apparatus and secrete formic acid. Males do not possess 
a poison. 

Wasps. — The digger wasps {Sphecoidea) are distinguished from 
the true wasps by their non-folded wings. They are solitary and 
place paralyzed insects and spiders in their nests, where the larvae 
feed on living helpless prey. 

The true wasps ( Vespoidea) include the solitary wasps and the 
social wasps. The solitary wasps {Eumenidae) resemble the digger 
wasps in that they form burrows. They deposit their eggs and then 
abandon them. (Consult Taylor, L . H., 1922, Psyche, vol. 29, 
no. 2.) The social wasps ( Vespidae) include t\v^ yellow jackets and 
hornets. The queens have stings but the males are harmless. Social 



ipS ARTHROPODA 

wasps feed the young continually through the larval stage of about 
two weeks. The white-faced hornet makes a large paper nest. 

The Chrysidoidea are parasitic Hymenoptera, about one-half inch 
long, feeding on larvae of other Hymenoptera, or on the stored food 
in their nests. 

Bees. — The Apoidea include the bees. Bees are stouter bodied 
than wasps and usually hairy. Their tarsal segments are flattened 
and enlarged for carrying pollen. 

The short-tongued bees are either solitary or gregarious, but never 
social. Most of them are mining bees, sinking perpendicular shafts 
a foot into the ground of grassy fields. The long-tongued bees 
{Apidae) have the lower lip greatly developed for securing nectar. 
The leaf cutter is a solitary species depositing her eggs in a hole in 
some trees, with a supply of pollen and nectar for the young, and 
then abandoning them. The guest bees {Psithyrus), regarded as 
degenerate bumble-bees, have no worker forms but infest the nests 
of solitary bees. 

The social bees or " bumble-bees " {Bombus) live in communities 
like the ants. They are important in the pollination of clovers. 
(See page 484.) The queen usually starts her nest in a deserted 
mouse's nest. The honey bee {Apis mellifera),^ a native of Europe, 
has been domesticated the world over for centuries. There are 
two genera, one stingless, the other including our common hive bee. 
The colony consists of queens, drones and neuter workers. The 
queen is fed on " royal jelly," which is a nutritious fluid excreted by 
the nurses. The bee is able to lift and carry about twenty-five 
times its own weight (Figure 93). 

Honey. — For centuries honey has been used for food and at the 
present time the United States produces about 250,000,000 pounds 
of honey annually. Although it is reported to be lacking in vitamins 
and minerals, honey is esteemed as a delicacy and is used in the 
preparation of medicines and candies. 

"The honeys of Hymettus and of Hybla were especially famous 
In ancient times; and both retain to the present day their char- 
acteristic flavor of wild thyme." (Consult L. Whibley, "A Com- 
panion to Greek Studies." Cambridge University Press, 1905.) 

* Alpatov, W. W., 1929, furnishes a new classification of bees in "Biometrical stud- 
ies on variation and races of the honey bee {Apis mellifera)". Quart. Rev. of Biol., 
vol. 4, no. I, pp. 1-58, March. Vergil, in one of the finest passages of ancient poetry 
(Georgics, Book IV), treats of the culture of bees. He discusses the placing of hives, 
the managing of swarms, and describes a battle between two discordant "kings." 



ARTHROPODA 



199 



In Northern Asia Minor poisonous honey has recently been 
reported. This phenomenon was described earlier by Xenophon 
and Aristotle. The bees are supposed to secure toxic nectar from 
two species of rhododendron. The toxic honey causes giddiness 
and sometimes a brief loss of consciousness, followed by a short 
period of general malaise " as though one had been on a spree." 




Worker Queea JDrone 

Fig. 93. Worker, queen, drone. (From Phillips, U. S. D. A. Farmers Bull. 447.) 

Methods of Insect Control. — Insects are controlled by poisons 
acting through the alimentary canal or by contact. Sucking insects 
are controlled by contact poisons while biting and chewing insects 
are controlled by internal poisons. 

Contact Insecticides. — In the adult condition, the chief sub- 
stances used as contact insecticides against sucking insects, such as 
flies and bugs, are lime sulphur wash, whale-oil soap, kerosene 
emulsion, tobacco decoction, miscible oils, pyrethrum, lime dust, 
commercial sodium fluoride, carbolic acid emulsion, and white 
arsenic. In the case of aquatic larvae like those of the mosquito, a 
thin film of oil or a thin coating of some substance like Paris green 
or pyrethrum proves effective. 

Stomach Poisons for Biting Insects. — In the case of the biting 
insects attacking trees and vines, it is customary to spray or dust 
with active poisons such as Paris green, arsenite or arsenate of lime, 
arsenate of lead, hellebore, or sodium fluoride. Arsenate of lead 
is used in preference to Paris green. 

The Use of Gases. — Repellants such as naphthalene are used to 
drive insects away. Lime repels the striped cucumber beetle, while 



200 ARTHROPODA 

whitewash containing a repellant chemical is used on tree trunks to 
drive away the egg-laying adults of borers. The poisonous gases 
most commonly used as fumigants in insect control are carbon 
bisulphide, naphthalene, hydrocyanic acid gas, sulphur dioxide, 
tobacco, formalin and carbon tetrachloride. Young trees are 
usually fumigated when imported into a state or received from a 
foreign country. In the orchard, trees are covered with tents and 
fumigated. 

Temperature Control. — Fall cultivation with reference to the 
susceptibility of the animal to low temperatures proves beneficial in 
killing wire worms, potato beetles, tomato worms and grasshoppers. 
Superheating will kill most of the flour mill insects. The Mediter- 
ranean fruit fly is limited to a temperature above 50° F., so will 
probably never get a foothold in any but our Southern States. 

Burning. — As weeds are likely to harbor injurious insects, they 
should be destroyed. Larvae and adults of garden and orchard 
pests are burned with the infested brush and vines. 

Natural Enemies. — Sometimes pests are imported into a new 
territory without the simultaneous introduction of their natural 
enemies. It is then necessary to find the most important forms that 
prey upon them. Such has been the province of explorers working 
for the United States Department of Agriculture. 

Next to the insects themselves, the birds are our most effective 
insect enemies.^ Some of the most important are the quail, the 
robin, the cuckoo and the sparrows. Even the despised crow more 
than pays for the small amount of corn that he eats. Measures 
that prevent the multiplication of wild races of cats will prove ef- 
fective in the protection of the birds. 

Other Protective Measures. — Valuable lumber is sometimes 
stored under water in order to prevent the action of wood borers. 
The use of fertilizers to stimulate plant growth may hasten develop- 
ment so that the plant will be able to resist an insect attack. To 
protect from the tent caterpillar, trees are frequently banded with 
tar and wrapped in burlap. Crop rotation and early lure crops 
often rid a plot of potato beetles. Ballou of the U. S. Department 
of Agriculture discovered (1928) that after a meal of geranium 
leaves or petals, the Japanese beetle becomes paralyzed. Post- 
mortems on the 35 per cent of paralyzed beetles which died inside 

® Strickland, E. H. 1928. Can birds hold injurious insects in check? Sc. Men., 
vol. 26, pp. 48-56. 



ARTHROPOD A 201 

of twenty-four hours showed that the digestive tract is destroyed in 
that time, and that all soft parts of the body cavity are disintegrated 
in forty-eight hours. The geranium is particularly attractive to the 
Japanese beetle. 

Class 5. Arachnida. — These air-breathing Arthropoda have no 
antennae, or true jaws; have the head and thorax fused into a 
cephalothorax; and at the posterior part the abdomen; and have 
four pairs of walking legs, with their first pair of appendages de- 
veloped into nippers, or chelicerae. They include spiders, mites, 
ticks, scorpions, and the king crab. 

Scorpionidae. — The scorpions are found in warm regions hiding 
away during the day and coming forth at night to prey on insects 
and spiders, which they sting with their poison fang at the tip of the 
abdomen. The sting of an ordinary scorpion of three or four inches 
has been compared with that of a hornet. Patten believes that 
scorpions are descended from the fossil Merostomata {Eurypterida). 
(See pages 207, 218.) 

Phalangidea. — The harvest men or " daddy-long-legs " have 
extremely long legs and a segmented abdomen. They feed on 
living insects. 

Acarina. — The common red mite and the " red spider " of green- 
houses attack plants. The chiggers or harvest mites attack mam- 
mals, including man, burrowing into the skin and causing much 
irritation. The follicle mite, Demodex folliculorum, invades the hair 
follicles of mammals and man, producing black heads. The itch mite 
is a parasite of the epidermis. The scab parasite, Psoroptes com- 
munis, produces sores on cattle and horses. 

Ticks are responsible for the transmission of a number of diseases. 
The cattle tick, Boophilus {Margaropus) annulatus, is the medium of 
transfer of a sporozoan, Piroplasma bigeminum, which causes Texas 
fever. In Africa, a common tick, Ornithodorus moubata, has habits 
like a bed-bug and causes relapsing fever. 

Older Araneida. (Spiders.) — Spiders (Figure 94) are among the 
most interesting of the Arthropoda. They construct webs, using two 
kinds of silk, one dry and inelastic, the other viscid and elastic. 
Spiders use silk to construct webs, to build tents or nests, and also 
in locomotion. Man uses spider threads for cross-hairs in his 
telescopes. Spiders are Arachnids, with the abdomen separated 
distinctly from the cephalo-thorax, but the segments of each region 
closely fused They have four pairs of legs and two pairs of mouth 



202 



ARTHROPODA 



parts. The mandibles or chelae are large and end in a slender, 
sharp-pointed hollow fang, through which poison flows. The palpi 
{pedipalpi) are sometimes half as long as the legs. 

The trap door spiders^ Cteniza^ dig tunnels, line them with silk. 




13 ^2 14 18 

Fig. 94. Internal anatomy of a spider. /, mouth; 2, sucking stomach; j, ducts 
of liver; 4, so-called malpighian tubules; 5, stercoral pocket; 6, anus; 7, dorsal muscle 
of sucking stomach; <?, caecal prolongation of stomach; g, cerebral ganglion giving off 
nerves to eyes; 10, suboesophageal ganglionic mass; //, heart with three lateral openings 
or ostia; 12, lung sac; /J, ovary; 14, 15, 16, 17, silk glands; 18, spinnerets; ig, distal 
joint of chelicera; 20, poison gland; 21, eye; 22, pericardium; 23, vessel bringing blood 
from lung sac to pericardium; 24, artery. (From Sedgwick, Textbook oj Zoology. 
Courtesy of Macmillan and Co., Ltd.) 



and equip them with a 
hinged lid. The ground 
spiders., Drassidae, deposit 
their eggs in silken tubes 
and do not spin a web. 
The jimnel web weavers, 
Agalenidae, weave concave 
sheets of silk with a funnel 
on one side, attaching the 
web to blades of grass by- 
threads. After a heavy 
dew, the webs are conspic- 
uous on the lawn or in the 
field. The cobweb weavers 
( Theridiidae) are small, 
light-colored forms, hang- 
ing downward from shape- 




FlG. 



95- 



Epeira, a garden weaver. 
A. M. Reese.) 



(Photo by 



ARTHROPODA 203 

less mazes of threads, frequently spun in corners of rooms. The 
orb weavers^ Epeiridae (Figure 95), construct webs that are mar- 
vels of efficiency, and sometimes span streams twelve feet wide. 

Poisonous Spiders. — The b/ack widow spider has caused a num- 
ber of deaths. Kellogg states (191 5) that a diadem spider of 1.4 gr. 
contains sufficient poison to destroy completely all the blood cor- 
puscles in 2.5 litres of rabbit blood. Comstock says that the 
tarantula^ frequently found in bunches of bananas, is incapable of 
seriously injuring man. 

Bibliography on Venomous Spiders 

Baerg, W, J. 1923. The effects of the bite of Lactrodectes mactans. 

Jour. Parasit., vol. 9, pp. 161-169, March. 
Bogen, E. 1926. Arachnidism, spider poisoning. Arch, of Int. Med., 

vol. 38, no. 5, pp. 622-632, Nov. 15. 
Comstock. The Spider Book. 

Kellogg, V. L. 191 5. Spider poison. Jour. Parasit., vol. i. 
Lloyd, J. S. 1921. Spiders used in medicine. Sc. Amer. Mon., vol. 

60, July. 
Reese, A. M. 1921. Venomous spiders. Sc, vol. 54, no. 1399, Oct. 

21. 

Reese, A. M. 1929. Economic Zoology. 3d Edition. 

Other Classes. Xiphosura. — The king crab or horseshoe crab 
(Figure 96), is the only living representative of an ancient group. 
Related fossil forms from the Carboniferous indicate that it origi- 
nated in fresh water. The horseshoe crab, Limulus, is a large 
marine form (2 feet long), commonly found on our Atlantic coast. 
It lives in shallow water and feeds on worms. It has a large 
cephalo-thorax and a relatively large abdomen with a long caudal 
spine. It is used for fertilizer and to feed hogs. It is particularly 
interesting to us because of the theory of the origin of vertebrates, 
developed by William Patten. (See p. 218.) 

Pycnogonida. — Sometimes classed as relatives of the Arachnids, 
these marine forms have four somewhat primitive eyes resembling 
those of spiders. They have a slender cephalo-thorax and abdomen 
and four pairs of jointed legs with seven or eight segments each. j 

The alimentary canal extends as ceca^ into the legs. Organs of / /^X6 
respiration are absent. The ma/es have four to seven cement glands " 

on certain of their appendages, usually the third. The secretion 



204 



ARTHROPODA 



cements the legs together in masses which are carried on the 
" ovigerous " legs of the male, and in one species on the female. 
The nervous system consists of cerebral, subesophageal and three 
other thoracic ganglia with two pairs of abdominal ganglia. Meta- 
morphosis usually occurs. The larvae of one genus are parasitic 
on the Coelenterata. They have no economic significance. 





Fig. 96. Limiilus polyphemus, the king-crab. A, dorsal view. /, carapace; 2, 
meso- and meta-soma; j, telson; 4, median eye; 5, lateral eye. B, ventral view. 
/, carapace; 2, meso- and meta-soma; j, telson; 4, chelicera; 5, pedipalp; 6, 7, 8, g, 
3d to 6th appendages, walking legs; 10, genital operculum turned forward to show 
genital aperture; //, 12, /j, 14, IS-, appendages bearing gill books; 16, anus; //, mouth; 
/<?, chilaria. (From Shipley and McBride. Courtesy of Macmillan and Co., Ltd.) 

Tardigrada. — The Tardigrada, slow-moving forms called " water 
bears " are small soft-skinned animals living in fresh and salt 
water or damp moss. They have four pairs of short-hooked, un- 
jointed legs. The digestive tract is well developed, the buccal cavity' 
containing teeth sometimes calcified. Their muscles are non- 
striated. No respiratory or circulatory organs are developed. The 
gonads are saccular and empty into the rectum. The nervous 
system consists of cerebral ganglia, and a nerve cord with four 
ventral ganglia. 



General Consideration of the Arthropoda 

Chaxacteristics and Distribution. — Deep sea Crustacea are huge 
in size and have a brilliant red coloring. Some are phosphorescent. 



ARTHROPODA 205 

Many aquatic forms are microscopic in size. Except in certain 
fixed forms, like the barnacles and parasitic forms like Sacculina, 
we find bilateral symmetry. 

The Arthropoda walk, leap, burrow, swim, and fly, with loco- 
motor organs and accessory structures correspondingly developed. 

Geographically they are most cosmopolitan. In the Island of 
Cyprus, certain centipedes are found on the burning plains and in 
the snows of the mountains. A fresh water crustacean, Lepidurus 
glacialisy is found only in the Arctic regions. The brine shrimp 
Artemia salina is found in brackish water and in pans of exceedingly 
salty water evaporating in the sun. In certain hot springs, crus- 
taceans and insect larvae live at a temperature of 60° C. 

Integument and Musculature. — The skin of the Arthropoda con- 
tains epidermal cells (pigmented membrane of the lobster) which 
secrete a chitinous exo-skeleton frequently containing lime salts, 
but found to be extremely thin at the joints. Chitin is anhydride 
of dextrosaynine^ a sugar derivative. Growth is in most cases ef- 
fected by a process of ecdysis or moulting^ in which the old shell 
cracks off and the new skin rapidly hardens. The period just after 
moulting is a most dangerous one for most Arthropoda, for their 
brethren are cannibalistic. Under the epidermis we find connective 
tissues and the dermis with nerves and blood vessels. 

Circular muscles found in the Annelida are absent in the Arthro- 
poda, the longitudinal muscles causing movement of the segments. 
The appendages are well supplied with muscles. 

Digestive System. — In parasitic forms the mouth may be ex- 
tremely rudimentary. The wide difference in mouth parts of in- 
sects gives a basis for their classification. The digestive tube varies 
much with the type of food consumed. Crustacea like the lobster 
have a short gullet leading to a large cavity, the stomach, which has 
a gastric mill for gizzard-like grinding. 

In insects with mandibles (grasshoppers, crickets, and locusts) 
we find a well-developed gizzard. In the insects there is great 
variation in the form and length of the digestive tube. In carniv- 
orous species the crop, gizzard and large intestine are sometimes 
absent. In bees the crop is the " honey-bag." There is no true 
liver in the insects, but the functions of a hepato-pancreas are per- 
formed by glands in the stomach. 

In spiders the pharynx and gullet are extremely small and the 



2o6 ARTHROPODA 

alimentary canal Is short and straight. The stomach and intestine 
send out lateral tubular or bladder-like expansions. 

There are many species o^ parasitic Arthropoda. Fish lice (crus- 
tacea) are external parasites and suck in nourishment. Rhizo- 
cephala, such as Sacculina, send ramifying absorptive roots through 
the body of the host. But in insects and arachnids we find parasi- 
tism most highly developed. 

Respiration.^" — In water-breathing Arthropoda we find modified 
appendages (gill-books of the king crab) or well-developed gills 
such as in the lobster. The air breathers have a highly developed 
tracheal system opening to the exterior by paired spiracles or 
stig?7iata. 

Circulatory System. — The system of circulation of Arthropoda is 
not closed but an open one with sinuses playing an important part in 
the collection of impure blood. The heart is usually elongated and 
dorsally situated in Arthropoda. The Crustacea (lobster) have a 
shield-shaped heart just posterior to the stomach. The blood enters 
t\vQ pej'icaj-dial iinus and passes into the heart by several pairs of ostia 
which have valves. Arteries leave the heart and pass to the inter- 
cellular spaces. 

The orange color of the blood of the prawn, and the yellow 
color of the insects' blood are perhaps due to carotene, according 
to A. C. Redfield. The green blue color of the blood of a lobster 
is due to hemocyanin. 

The role of carotene, a highly unsaturated hydrocarbon (CgoHse) 
as an important agent in holding and slowly emanating absorbed 
radiant energy, is a subject that interests the author of this text. 
(P. 442.) 

Excretion. — In Insects and Arachnids there are excretory tubules 
(Malpighian tubules) which communicate with the intestine. In 
the lobster and allied Crustacea, the paired green glands send their 
secretion out from pores at the bases of the antennae. 

Nervous System. — In Arthropoda the cerebral and sub- 
esophageal ganglia have developed highly. We also find that the 
thoracic ganglia are large and show the efi'ects of a lateral fusion. 
The nerves in the thoracic region are especially well developed. On 
the whole the nerve cord reminds one of that of the Annelid but is 
more highly developed. 

*° Lee, M. O. 1929. Respiration in the insects. Qu. Rev. of Biol., vol. 4, no. 2, 
pp. 213-232. 



ARTHROPODA 



207 



Sense Organs. — Tactile and olfacto-gustatory senses are ex- 
tremely well developed in the group. ^^ Equilibratory organs 
(otocysts) are found at the base of the antennules in the Crustacea. 
In the mosquito we find auditory vibratile hairs, while the grass- 
hopper has specialized tympani^ with nerve cells for the reception of 
sound waves. 

Vision is accomplished by two kinds of eyes, simple ones called 
ocelli^ and compound ones. The compound eye consists of om- 
matidia arranged radially around the end of the optic nerve. Each 
ornmatidium consists of an external cornea (facet), a cellular cone- 
like lens, sensory retinal cells which receive the light, and pigment 
cells which separate the retinal elements of the ommatidia from each 
other. 




Fig. 97. Three trilobites. A, a Cambrian species; 5, a Devonian species, showing a 
compound eye; C, an Ordovician species. (From Norton, Elements of Geology.) 

Fossil Relatives. Eurypterida (Merostomata) .—This order is 
linked with Limulus by many Paleozoologists. Specimens six feet 
long are found in strata from the Cambrian to the Carboniferous. 
The head is small and unsegmented, bearing two lateral compound 
eyes, two median ocelli, and six pairs of gills, covered by plates. 

" In insects the chemical sense is much more highly developed than in man. The 
mouth parts and tarsal segments of the red admiral butterfly {Pyrameis atalantd) are 
256 times as sensitive to saccharose as the human tongue. Olfaction in the bee is keen; 
but the bitter substances such as quinine are readily accepted when mixed with saccha- 
rose. (D. E. Minnich. 1929. The chemical senses of insects. Qu. Rev. of Biol., 
vol. 4, no. I, pp. 1 00- 1 12, Mar.) 



2o8 ARTHROPODA 

Patten considers that Paleozoic Eurypterids have scorpions as their 
survivors and that the Ostracoderms represent their fossil descend- 
ants, which led towards the true Vertebrates. (See page 219.) 

Trilobita. — The extinct trilobites (Figure 97) were dominant 
species in the Cambrian period, but disappeared in the Carboni- 
ferous. The limbs resembled those of Crustaceans and antennae 
were present. It has been suggested that trilobites descended from 
a stock common to Arachnoidea and Crustacea. 

Arachnoidea. — The scorpions are represented in the Silurian 
rock by fossil forms similar to those now living. All living Arach- 
noidea are represented in Tertiary deposits. Crustacea are abun- 
dant as fossils, from the early Paleozoic. Myriapoda are found 
from the Devonian. Insecta appeared in the Pennsylvanian. 



CHAPTER XIII 

Chordata 

Classification 

Subphylum Hemichorda (Enteropneusta). 
Subphylum Urochorda (Tunicata or Ascidia). 
Subphylum Adelochorda (Acrania). 
Subphylum Vertebrata (Craniata). 

Class Cyclostomata. 

Class Pisces. 

Class Amphibia. 

Class Reptilia. 

Class Aves. 

Class Mammalia. 

The Phylum Chordata Includes not only common Vertebrate 
animals such as Fishes, Amphibia, Reptilia, Birds and Mammals, 
but also includes certain marine forms that are extremely significant 
in discussions of the probable origin of Vertebrates from Inverte- 
brates. 

The name Chordata is derived from the notoc/iord, which is 
found at some stage of the existence of all Vertebrates, but is per- 
sistent in the adults of those intermediate types that we will shortly 
proceed to describe. The notochord is a long, cylindrical, double- 
pointed rod, which is located ventral to the nerve cord. Notochor- 
dal tissue consists of large vacuolated cells (somewhat resembling 
the pith of plants) with their nuclei confined to the dorsal and 
ventral regions. The vacuoles of these cells are filled with liquid 
which renders them turgid. The notochordal sheath is extended 
dorsally to enclose the nerve cord. 

Comparison of Vertebrates and Invertebrates 

Up to the present time we have been dealing entirely with the 
Invertebrates. It is therefore desirable, before we go further with 
the animal phyla, to compare briefly the Invertebrates with the 

209 



2IO CHORD AT A 

Vertebrates, pointing out the distinguishing features which mark 
an advance in the Vertebrate type. 

Invertebrates versus Vertebrates 

Dorsal heart. Ventral heart. 

Solid nervous system. Tubular dorsal nervous system. 

No endoskeletal structures. Either a notochord or a vertebral column. 

There is no Class of the Invertebrate Metazoa whose characters 
have not been repeatedly suggested to reveal affinities with the 
Vertebrates. 

Before discussing the different theories of Origin of the Verte- 
brates, it will be best to take up the anatomy of examples of the 
Hemichorda, Urochorda and Cephalochorda, since these are con- 
sidered by some to be connecting types. 

Subphylum Hemichorda. (Enteropneusta.) Characteristics. 
(Balanoglossus.) — i. Hollow, tubular notochord, opening into a 

straight alimentary canal. 

2. Gill slits. 

3. Dorsal blood vessel and anterior 
(dorsal) heart. 

4. Dorsal and ventral nerve strands, 
with many nerve fibers and scattered giant 
nerve cells. 

The genus Balanoglossida includes 

Balanoglossus {Dolichoglossus) kowalevskii. 

This form is divided into three regions, 

the proboscis^ the collar, and the trunk. 

The proboscis, when distended with water, 

serves as an organ for burrowing in the 

mud. Gill slits open into the anterior end 

of the straight alimentary canal. The 

paired hepatic cecae are located near the 

posterior end of the digestive tube. The 

dorsal and ventral blood vessels receive 

blood from the anterior heart. Excretions 

are extracted by the kidney, which sends 

its wastes out through the proboscis-pore, 
Doscis; 2, collar; ?, giu-siics. . , , n 1 n • j t-i 

(After A. Agassiz. Courtesy With Other expelled fluids. The sexes ^ are 

of Henry Holt & Co.) separate and the ger7n cells, formed in a 




Fig. 98. Balanoglossus. 
Linville and Kelly. /, pro- 
boscis; 2, collar; j, gill-slits. 



CHORDATA 



211 



double row of ovaries or testes, are extruded through pores in the 
body wall. (Figure 98.) 

Some species of Balanoglossidae have a ciliated larva called the 
Tornaria, which was once considered a larval Rchinoderm. (See p. 
217.) Cephalodiscus and Rhadopleura are colonial Hemichorda, 
which reproduce by buds. Both these forms were at one time re- 
garded as Polyzoa. They have small probosces, and their alimen- 
tary canals are bent. Both are deep-sea forms. 

Subphylum Urochorda. (Tunicates, Sea Squirts, Ascidians.) 
Characteristics. — i. Retrogressive metamorphosis. 

2. Multiplication by budding, as well as by gonads. 

3. Reversal of the heart beat. 

4. A tunic or mantle composed of cellulose (CeHioOs). 

Adult sea squirts (Figure 99, A, B, C, D, E, F) resemble the 
siphonate molluscs in the possession of incurrent and excurrent ori- 
fices and a mantle. The Tunicates hence were long associated with 




Molgula 
manhattensis 




Molgula 
arenata 




Eugyra 
pillularis 




Botryllua 
gouldii 




Cynthia partita 




Salpa cabotii 



Fig. 99. A group of Urochorda. J, Molgula manhattensis. B, Molgula arenata. 
C, Eugyra pillularis. D, Cynthia partita. E, Botryllus gouldii. F, Salpa Cabotii. 
(From Verrill.) 



212 CHORD ATA 

the molluscs. Later, they were associated with the worms. Their 
development, however, shows them to be related to the Vertebrates. 
The larval ascidian is more highly developed than the adult. 

Anatomy and Physiology. — The tunic or mantle has the same 
chemical constituents as cellulose (CeHioOs). Nowhere among 
animals is there such a rich formation of cellulose. The anterior 
part of the digestive tract is modified into a pharynx or branchial 
chamber, the walls of which are perforated by a number of gill 
slits leading to the exterior, or to a peri-branchial chamber, and from 
this to a cloaca. While respiratory water passes through the gill 
slits, the food particles which it contains are received by a ring- 
shaped ciliated band and, enveloped by mucus, are led to the esoph- 
agus. The mucus is formed by a ciliated glandular groove, the 
endostyle on the ventral surface of the pharynx. The ventral tubular 
heart lies in the pericardium between the gill region and the stomach. 
It changes the direction of its contractions frequently, first driving 
the blood to the gills, then resting; then pumping it from the gills 
and sending it to the stomach. The ductless excretory organs are 
in the second loop of the intestine; the dorsal ganglion and the 
subneural gland are the only remains of the comparatively well- 
developed brain of the larva. The subneural gland which is asso- 
ciated with the dorsal ganglion is homologous to the hypophysis ^ 
of the higher vertebrates. The gonad is hermaphroditic, the testis 
surrounding the ovary, and the animal is first a female, then after 
pregnancy becomes a male. The larva of the ascidians is active, 
swims by a long tail, looks like a tadpole, and has a notochord. 
(Figure loo.) 

Description of the Larval Ascidian. — The tail is fringed with a 
caudal fin which is an outgrowth of the thin test covering the whole 
surface. The notochord is in the axis of the tail. The nerve cord is 
dorsal and forms the trunk ganglion and sense vesicle with otocyst 
and eye. The digestive system consists of pharynx, esophagus, 
stomach and intestine. The larva remains only a few hours in the 
tailed free swimming stage. Then It becomes fixed by adhesive 
papillae and begins to undergo retrogressive metamorphosis. 
Molgula manhattensis (which has no tailed form) reaches its full size 

^ Butcher (1930), Jour. Exp. Z06I., vol. 57, no. i, pp. i-ii, has shown that in 
Molgula manhattensis the pituitary gland has the oxytocic principle of posterior pitui- 
tary. (See page 448.) 



CHORDATA 



213 



of one inch in about six weeks. Botryllus (the star-spangled jelly) 
is a compound ascidian ranging from New Jersey to Maine. 

Economic Importance. — The sea squirt or " sea-peach " is eaten 
in South America and the Mediterranean countries, but is said to 
taste rather bitter. 




Fig. 100. Internal anatomy of the adult sea squirt. (Courtesy of Amer. Mus. of 

Nat. Hist.) 



214 



CHORDATA 



•^j 



/ 



■o 



>o 



Subphylum (Cephalochorda, Adelochorda, 
or Acrania). Type — Branchio stoma ^ or 
Amphioxus. — Amphioxus, the lancelet, is 
transparent, less than three inches long, lives 
in shallow sea water, partly buried in sand, 
burrows head foremost, swims at night. 
Beebe reports them in the Sargasso Sea. 
(Figure loi.) 

It has a median dorsal fin, extending 
posteriorly to form the caudal fin and then 
ventrally to the post-atrial region to form 
the ventral fin. The laterally situated meta- 
pleural folds occupy the position of lateral 
fins in fishes. 

Body Wall. — The outer covering is a 
single layer of columnar epithelium cells, 
the epidermis., with sensory cells, goblet cells 
(unicellular glands) and ciliated cells. The 
dermis consists of soft connective tissue. 

Muscular Layer. — The muscular layer 
has strikingly definite metameric segmen- 
tation. The myomeres, myotomes or muscle 
plates are alternately arranged on the right 
and the left sides permitting flexible lateral 
movements and with connective tissue septa 

2 Balanoglossus, the Tunicates, and Branchiostoma 
have the following characteristics in common at some 
stage in their existence: (i) notochord; (2) pharyngeal 
gill slits; (3) dorsal nervous system. 



Fig. ioi. A lateral view of Amphioxus (trans- 
parency), a, anus; «./>., atrial pore; f./., caudal fin; 

^&D cir., cirri, on the edge of the vestibule leading to the 
mouth; ^./., dorsal fin; r, fin rays; g, gill of branchial 
structures consisting of alternate slits, through which the 
water passes, and supporting plates, in the walls of 
which are the blood vessels; in., intestine, from which 

: as a diverticulum springs /, the liver; m, the mouth sur- 

rounded by a fringed velum; my., myotomes or muscle 
segments; n.c, notochord; 0, ovaries; s.c, spinal cord; 

'G ^•/•> ventral fin. (From Galloway. Courtesy of P. 
Blakiston's Sons Co.) 



CHORDATA 



215 



called myocommas. The dorsal body wall is greatly thickened as 
it is in all Chordates and contains the hollow nervous system and 
the notochord. The notochordal sheath of connective tissue is 
produced dorsally into a covering for the canal containing the nerv- 
ous system. The cells are 
turgid with fluid. 

Digestive System . — The 
mouth has ciliated oral cirri, 
with tactile sensory cells. 
The twelve velar tentacles 
extend as strainers from the 
velum across the mouth. 
The pharynx with its one 
hundred pairs of gill slits 
functions in respiration as 
well as digestion. The epi- 
branchial groove is ciliated, 
dorsally indenting the phar- 
ynx, and the ventrally situ- 
ated endostyle (Figure 102) 
(hypobranchial groove) fur- 
nishes mucus which entangles 
food particles. The food is 

carried by the cilia of the „ _ .• ^ ^i- ,, 

•^ . Fig. 102. Cross-section Amphioxus. 

epibranchial groove to the m- Hertwig-Kingsley. a, aorta descendens; b, 
testine. The liver, attached peribranchial space; c, notochord; ro, coelom 
to the anterior end of the (branchial body cavity); e^ hypobranchial 
intestine, protrudes into the groove, beneath It the aorta ascendens; g, 
1 1 ;,.,, TU^ V,o gonad; ^^, gill arches; ^i, pharynx; /, liver; »7, 

pharyngeal cavity. Ine he- & ' '^ ' '^ ^ 

^ ■' ° . •J- • muscles; «, nephndia, on the lert with an 

patlC secretion is a digestive ^..^w; r, spinal cord; .«, spinal nerve; .;>, gill 
juice probably analogous to glit. (After Lankester and Boveri. Courtesy 
the secretion of the pancreas of Henry Holt & Co.) 
of the vertebrates. 

Respiratory System. — The atrium is a wide chamber between the 
body wall and the pharynx into which the gill clefts lead. As in the 
tunicates the cilia lining the gill clefts produce a current setting in 
at the mouth, entering the pharynx and passing thence by gill slits 
into the atrium and out the atriopore. The current is for respiration 
as well as food. The coelom consists of paired cavities in the pharyn- 
geal region connected by narrow canals in the gill folds with the 
endostyle. 




21 6 CHORD ATA 

Circulatory system consists of a dorsal vessel (paired and un- 
paired dorsal aortae); a ventral vessel (subintestinal vein and ven- 
tral aorta); and commissural, connecting, afferent and efferent 
branchial arteries with intestinal capillaries. The circulation differs 
from that in the Annulata, since the blood in the ventral vessel 
travels forwards and the blood in the dorsal vessel travels backwards 
which is the opposite from the condition in the Annelida. All the 
intestinal blood passes through the liver before reaching the ventral 
aorta. The hepatic portal system is characteristic of all verte- 
brates. The blood is almost colorless with no leucocytes and but 
few erythrocytes. 

Excretory System. — There are 90 pairs o( nephridia situated above 
the pharynx. Columnar and excretory cells are situated on the 
floor of the atrium. 

Reproductive System. — The sexes are separate, 26 pairs o{ gonadial 
pouches opening into the atrium. The ripe germ cells burst from the 
inner walls of the gonadial pouches and escape by way of the atrium 
and atriopore to the external water where fertilization takes place. 

Nervous System. — The dorsal nerve tube has an axial cavity, the 
neurocele, which is dilated anteriorly to form the cerebral ventricle. 
The dorsal portion of this ventricle is dilated into a pointed pouch, 
the median olfactory lobe, while in the ventral posterior portion there 
is a depression probably corresponding to the infu7jdibulu7n of higher 
forms. A large number of spinal nerves come from the spinal cord. 
They arise alternately, in each segment, two dorsal nerves, sensory 
and motor, supplying the skin and transverse muscles; and two 
ventral nerves, purely motor, supplying the myotomes. 

Sense Organs. — The olfactory pit {hypophysis) is a ciliated depres- 
sion opening externally on the left side of the snout. The median 
cerebral " eye " has no lens and may not be sensitive to light. The 
socalled gustatory groove on the roof of the buccal cavity may not 
be an organ of taste. There are no equilibratory or auditory organs 
known. 

Kconomic Importance. — Vast quantities of the Amphioxus are 
used as food by the Orientals, particularly the Chinese. 

Theories of the Origin of Vertebrates 

Theories of the origin of vertebrates include the Amphioxus 
theory, the Annelid theory, the Nemertean theory and the Arthropod 



CHORDATA , 217 

theory. The higher phyla of Invertebrates have practically all 
been studied by investigators with the idea that affinities with the 
vertebrates could be determined. 

Amphioxus Theory. — The Amphioxus theory as developed by 
various workers and set forth by Willey is as follows. The ancestor 
of the vertebrates was a free swimming animal intermediate between 
the tadpole of the Tunicate and Amphioxus. It had the ventral 
mouth, pituitary and notochord (limited) of the Tunicate; and the 
myotomes, coelomic epithelium, and straight alimentary canal of 
the Amphioxus. The chief factor in the evolution of the verte- 
brates has been the concentration of the central nervous system 
along the dorsal side of the body and its conversion to a hollow tube. 
The hypophysis may have become evolved in connection with a 
functional neuropore. Adam Sedgewick and Van Wijhe suggested 
that the neural canal had as its original function the promotion of 
oxygenation of the tissue of the Central Nervous System, the water 
entering by the neuropore and leaving through the posterior neu- 
renteric canal. Harmer and Brooks suggested independently that 
the gill slits arose at first to carry away the bulk of water con- 
stantly entering the mouth with the food, obviating the necessity 
of the flow of water through the alimentary canal. Later they aided 
in performing the function of respiration. (Cephalodiscus has 
luxuriant branchial plumes, sufficient for respiration, and the pair 
of gill slits allow the water to pass from the pharynx.) The noto- 
chord occurs in Balanoglossus {Enteropneusta) in the proboscis; 
and in the tail of larval Tunicates. In Balanoglossus it may be a 
divergent structure. The notochord may have arisen as a solidi- 
fication of the endoderm, continued into the caudal portion of the 
body to afford axial support for a locomotor tail. Endoderm as a 
stiffening substance has been developed in some medusae and hy- 
droid polyps as there is skeletal tissue in their tentacles in the form 
of a solid endodermal axis. 

The Amphioxus theory supposes that Amphioxus was derived 
from a Tunicate (Ascidian) and that the Tunicate arose from a form 
possibly hke Balanoglossus. Balanoglossus may or may not have 
arisen from the Echinodermata. The ciliated Tornaria larva of 
Balanoglossus is similar to the larvae of the Echinoderms in that it 
possesses bilaterality, ciliated bands, pelagic life and is small and 
quite transparent. 

That the earlier fishes were similar to Amphioxus and that the 



21 8 CHORDATA 

higher fishes developed from the primitive type through the in- 
fluence of a rapid stream environment is the belief of T. C. Chamber- 
lain. 

Arthropod Theories. — The theory of Gaskell (1908) is based on 
the assumption that the whole alimentary canal of a crustacean-like 
Arthropod united with the nerve cord to form the hollow brain and 
spinal cord of the vertebrates. Gaskell's theory reflects his knowl- 
edge of physiology, but indicates his lack of training in comparative 
anatomy, embryology and paleontology. 

Patten's Arachnid theory was first published in 1889 in the 
Quarterly Journal of Microscopical Science, and was followed by a 
number of important papers preceding the publication of his book 
in 191 2. Dr. Patten has pointed out (personal communication, 
1 931) that the Arachnid theory gives a satisfactory explanation 
of the other theories of evolution of vertebrates while none of these 
theories explains the detailed resemblance between Vertebrates and 
Arachnids, 

The following summary was furnished by Dr. Patten (consult 
his article in the Quarterly Journal of Microscopical Science, vol, 
Si.PP- 317-378, 1890): 

"The Arachnid theory — 1890 — is based on the following evi- 
dence: (i) In the Arachnids, the first sixteen, or more, metameres 
form a characteristic pattern, consisting of five groups of highly 
specialized functions and organs, all of them different and all ar- 
ranged in a definite sequence. (2) This basic pattern is essentially 
the same as that in the "head" of vertebrates, and all the corre- 
sponding organs in each group have essentially the same structure, 
and develop embryologically in essentially the same ways. Some 
of the corresponding parts are the notochord and the endocranium, 
the main divisions of the brain, special groups of sense organs, 
nerves, ganglia, somites, gill sacs, and oral arches. (3) The marine 
Arachnids were the highest animals in existence during the long 
and very early geologic eras. In the Cambrian, or some pre-Cam- 
brian era, they apparently gave rise to the great class of Ostraco- 
derms, which are mainly Silurian; and they in turn gave rise to the 
true fishes, with united oral arches, which first appeared in the 
Devonian. Many peculiarities of the Ostracoderms, especially 
the structure of the exoskeleton and the oral arches, support this 
conclusion. (4) The Tunicates, Amphioxus, and other chordate 



CHORD ATA 219 

types, are regarded as defective, aberrant offshoots of the main 
vertebrate arachnid phylum." 

The recent discovery by Prof. J. Kiaer of well-preserved fossil 
Ostracoderms in the Silurian rocks of Norway, and the collection by 
Professor Stenso of perfectly preserved fossils of one of them, Cepha- 
laspis, from the Devonian rocks of Spitzbergen, have given new evi- 
dence to support Professor Patten, and gratified the friends of this 
"grand strategist of evolution.!' Serial sections of the Spitzbergen 
specimens studied by Patten indicate that the "radiating bony chan- 
nels for the cranial nerves, and many other architectural features of 
the anatomy of the head conform to the general plan seen in the 
heads of fossil Enrypterids and other arthropods." ^ 

Professor Patten has made three expeditions to the Island of 
Oesel excavating fossils and in 1931 found six new species of ostraco- 
derms.^ 

Annelid Theory. — The Annelid theory advanced by Dohrn, 
Semper, Beard and Delsman postulates that an annelid is turned 
over on its back and develops a mouth and anus. The notochord 
is represented in the annelids by a bundle of fibers running along the 
nerve chain, occupying a similar position to the notochord of the 
chordata and apparently serving the same function of support. 
Connective tissue encloses both nerve cord and fiber bundles 
(Faserstrang.) just as the notochord and the spinal cord are 
enclosed in the higher type. 

The segmentally arranged nephridia correspond to the primitive 
kidney tubes of the vertebrate kidney. The segmentally arranged 
ganglia around the appendages of some worms ( Nereis) may cor- 
respond to the branchial and lateral sense organs of the Ichthyopsida 
and the ganglia of some of the cerebral nerves. 

The fundamental relationship of the nervous system and the 
vascular system to the digestive tract as found in the annelids is 
quite comparable to the condition in the primitive vertebrates. 

Wilder has indicated the present trend away from the Annelid 
theory and points out that a worm-like ancestor does not necessarily 
mean that we must accept an annelid. (See trochophore, p. 125.) 

5 Gregory, W. K., 1928, in Creation by Evolution, edited by F. Mason, Mac- 
millan Co., New York. 

* Consult Patten, W., 1931, New Ostracoderms from Oesel. Science, vol. 73, 
no. 1903, pp. 671-673. Tremataspis has, as predicted, paired jaws or oral arches, like 
those in embryonic vertebrates (frog) and which work sidewise, not forward and back- 
ward as in the united oral arches of adult vertebrates. 



220 CHORDATA 

Nemertean Theory. — The Nemerteans, probably related to the 
Platyhelminths, were suggested as having affinities with vertebrates, 
by Hubrecht. His theory attempts to homologize the proboscis 
sheath of the Nemertean with the notochord of the chordate. He 
suggests that the vertebrate nervous system developed from the 
three nerve cords of a Nemertean. The dorsal nerve cord of the 
Nemertean became the central nerve system and the lateral nerve 
cords persist in the rami lateralis X, of the lower vertebrates. As 
the other organs of the animals are not similar in arrangement the 
theory seems of little importance. 

References on the Origin of Vertebrates 

Delsman, H. C. 1922. The Ancestry of Vertebrates as a Means of 
Understanding the Principal Features of Their Structure and 
Development. Weltevreden (Java). 

Gaskell, W. H. 1908. The Origin of the Vertebrates. London, 
Longmans-Green. 

Hubrecht, A. A. W. 1883. On the ancestral form of the Chordata. 
Quart. Jour. Micr. Sci., N.S., 23: 349-368. 

Lull, R. S. 191 7. Organic Evolution. New York, Macmillan. 

MacBride, E. W. 1914. Text-book of Embryology. Vol. i, Inverte- 
brate. London, Macmillan. 

Newman, H. H. Vertebrate Zoology. New York, Macmillan. 

OsBORN, H. F. 1917. The Origin and Evolution of Life. New York, 
Scribners. 

Patten, W. 191 2. The Evolution of the Vertebrates and their Kin. 
Phila., Blakiston. 

Patten, W. 1920. The Grand Strategy of Evolution. Boston, R. G. 
Badger. 

Wilder, H. H. 1909. History of the Human Body. New York, Holt. 



CHAPTER XIV 



Cyclostomata 



Craniata. — The Craniata include the vertebrates, from the eel- 
like lamprey, up to man himself. In all we find that in the embryo 
an axial notochord appears. This is persistent inside the centrum 
of the vertebra of an elasmobranch, but is replaced in higher forms 
by the true vertebral column. 

Classification. — 



I. 


Cyclostomata 


II. 


Pisces. 


III. 


Amphibia. 


IV. 


Reptilia. 


V. 


Aves. 


VI. 


Mammalia. 



Characteristics of Craniata. — i. Segmented animals without 
external ringing of the body but with metameric arrangement of the 
internal parts. 

2. A cuticular skeleton absent, but there may be a horny epi- 
thelium or dermal ossifications. (Scales, etc.) 

3. An axial skeleton is present; either a notochord or skull and 
vertebral column. Two kinds of appendages are supported by the 
axial skeleton, the unpaired fins of the fishes and amphibia and the 
paired fins, or limbs of the higher vertebrates. 

4. The central nervous system is dorsal and hollow and consists 
of cerebrum, midbrain, optic lobes, cerebellum, and medulla ob- 
longata, with the spinal cord attached. The eyes and ears are the 
most highly developed of the sense organs. 

5. The respiratory organs arise from the endoderm; gill slits are 
present in the embryo. In land forms, these are replaced by lungs, 
developed from the hinder part of the pharynx. 

6. The heart is ventral and consists of one or two auricles; and 
one or two ventricles. In gill breathers the blood in the heart is 
venous. Pulmonary respiration brings blood to the heart pure 

221 



222 



CYCLOSTOMATA 



from the left side. The sinus venosus brings the impure blood to 
the right side of the heart. Circulation is a thoroughly closed 

system. 

Cyclostomata. (Gr., a circle; a mouth.) — The Cyclostomes, 
forms just below the fishes, include hag-fish and lampreys, both of 
which somewhat resemble eels but differ in a number of essential 
characteristics. (Figure 103.) 




Fig. 103. Cyclostomes. Upper figure, Pacific hagfish, Bdellostoma dombeyi. 
X 3^. The light apertures along the sides are mucous canals, the dark ones are 
branchial openings. Middle figure, Atlantic hagfish, Myxine glutinosa. X K- The 
dots along the side are mucous pits; the left common branchial aperture is at *. Lower 
figure, sea lamprey, Petromyzon marinus. X 3^. (After Dean.) 



Characteristics. — i. No jaws. 

2. No lateral appendages. 

3. No scales. 

4. No masticatory apparatus; rasping tongue present. 

5. No atrial cavity. 

6. Have a median unpaired nostril and the first distinct ap- 
pearance of a head. 

7. Have round mouth closed by the tongue. 

8. Pocket-like gills. 

9. Persistent notochord. 

10. Vertebrae present, separated from notochord. 

11. The gonads discharge into the coelom. 

Myxinoids. — The hag-fishes produce slime and, when captured, 
" turn water into glue." They are all marine. They attack dis- 
abled fish and enter the gills or mouth. Their digestive apparatus 
is so large that one meal takes a long time to digest. Blind, they 



CYCLOSTOMATA 223 

hunt at night. They are hermaphroditic, with an ovotestis, but one 
sex always predominates. 

Petromyzontia. (Stone; suck in.) — The lampreys are found in 
both fresh and salt water, the marine species being larger. They 
are predaceous, true vertebrate parasites. (Brook lampreys are 
not parasitic.) The lamprey breathes through the mouth except 
when feeding, then through the gill clefts.^ Gage and Day of 
Cornell University showed that the lake lampreys have in their 
buccal glands an anticoagulating substance similar to " hirudin." 
(See page 116.) 

The larvae, once called Ammocoetes, resemble Amphioxus. They 
have a hood, median eye, endostyle, epibranchial groove (which 
becomes the esophagus). The endostyle becomes the thyroid gland, 
and the median fin specializes. 

1 Consult Gage, S. H. 1927. The Lampreys of New York State. Supp. to 
17th. Ann. Report, N. Y. State Cons rvation Commission. 

Gage, S. H. 1929. Lampreys and tiieir ways. Sc. Mon., vol. 28, pp. 401-416, 
May. 

Surface, H. A. 1897. Lampreys of Central New York. Bull. U. S, Fish. 
Comm., vol. 18, pp. 210-215. 

Wheeler, W. M. 1900. Development of Urinogenital Organs of the Lamprey. 
Zool. Jahrb., vol. 13, pp. 1-88. 



CHAPTER XV 

Pisces 

Classification 

Subclass Elasmobranchii. 
Subclass Teleostomi. 

Order 1. Crossopterygii. 

Order 2. Chondrostei. 

Order 3. Holostei. 

Order 4. Teleostei, 
Subclass Dipnoi. 

Characteristics 

1. Aquatic vertebrates. 

2. Breathe by gills (vascular outgrowths of the pharynx). In the 

Dipnoi a single or double swim bladder functions as a lung, 
and the air is received at the surface of the water. 

3. The swim bladder of the Teleostomi is used as a hydrostatic 

organ. 

4. There are two pairs of fins, pectoral and pelvic, and also unpaired 

median fins. 

5. The skin usually has numerous scales, formed from the dermis, 

but covered with epidermis which may produce enamel. 
Scales are suppressed in electric fishes, and rudimentary in 
some other forms. Glandular cells are also found in the skin. 
There are sensory mucus canals, for touch and chemical 
sense. Some fishes have well-developed poison glands near 
the fins. 

6. The lateral line organs along the trunk are for vibrations of 

low frequency. 

7. The muscle segments persist throughout life. There is no muscle 

in the dermis however. 

8. The gut ends in a cloaca in many; in others a distinct anus is 

situated in front of the genital and urinary apertures. 

224 



PISCES 



225 



9. The nostrils are paired; there are no posterior nares, so the organs 

are exclusively olfactory. 

10. There are no tympanic cavities or ear drums. 

11. The heart is two chambered with venous blood except in the 

Dipnoi where it begins to be three chambered and receives 
pure blood from the lung as well as impure blood from the 
body. 

Apart from the Dipnoi, the heart has one auricle, receiving 
impure blood from the body; one ventricle which drives it 
through the ventral aorta to the gills, whence the purified 
blood flows to the head and by the dorsal aorta to the body. 
There is a sinus venosus receiving the impure blood and 
sending it into the auricle and thence to the ventricle. 
The conus or bulbus arteriosus, located at the exit of the 
arterial trunk from the heart, becomes more bulbous in the 
Dipnoi, presaging the development of the distinct bulb of 
the Amphibian heart. There are no vena cavae, but there 
are two posterior cardinal vessels. 

12. The kidney is the persistent mesonephros. There is no distinct 

urinary bladder. (Small paired ones in some fishes.) 

Natural History 

Subclass Elasmobranchii. (Gr., a metal plate; Lat., a gill.) 
Characteristics. — The Selachii have a cartilaginous skeleton, 
placoid scales, gills covered (separate covers), heart with arterial 
cone, a spiral valve in the large intestine and no swim bladder. 
Sharks have triangular teeth with notched edges; dogfish have flat, 
diamond-shaped teeth. They are marine except one fresh water 
Nicauragan shark. (Figure 104.) 

The great white shark or " man-eater " {Carcharadon carcharius) 
grows to thirty feet in length. Usually found in tropical waters, it 
sometimes strays to the North Atlantic. It will follow ships and 
seize refuse and so occasionally gets a " man overboard." Until the 
summer of 191 6 all reports of attacks on man by sharks in American 
waters were branded as false. Whale sharks reach a length of fifty 
to sixty feet. They eat small fish, squids and shrimps, straining 
them out of the water by means of the gill rakers. The thresher 
shark has a much elongated upper lobe on its " super-heterocercal 
tail," which furnishes a powerful weapon and also drives the small 



226 



PISCES 




Nurse Shark 

Gingli/mostoma cirratum (Gmelin) 





Smooth Dogfish 

Mustelus canis (Mitchill) 



Hammer-head Shark 

Sphyrna zygaena ( Linnaeus) 



Sand Shark 

Carcharias littoralis 
(Mitchill) 



Spined Dogfish 

Squalus acanthias (Linnaeus) 





Tiger Shark 

Galeocerdo tigrinus 
(Miiller and Henle) 




Thresher Shark 

Alopias vulpes (Gmelin) 





Man-eater Shark 

Carcliarodon carcharias 
(Linnaeus) 




^Mackerel Shark 

Isurus tigris (Atwood) 

Fig. 104. Sharks of various types. (After Nichols and Breder. Courtesy of N. Y. 

Zoological Society.) 



PISCES 



227 



fish together. Angel sharks are transition types between sharks 
and the skates and rays. They have large pelvic and pectoral fins, 
extending laterally. (Figure 105.) Rays and skates are much 
flattened dorsiventrally. They vary in size from the small " rugs" 
of the New Jersey coast to large skates eight feet in diameter. 
(Figure 106.) 

In the electric ray {torpedo-ray) modified muscle plates called 
electropaxes are developed from the muscles of the pectoral region. 
They are under control of the ray and connected with nerve centers 
in the medulla. The whip-tailed or sting-rays have tails armed with 
barbed spines, eight to nine inches long. At the base of the spines 
poison is secreted which entering the wounds made by the tail 
causes severe inflammation. Eagle rays may reach a width of 
twenty feet. The animal envelops prey with its " wings." Pearl 
divers have been drowned by these " sea vampires." Sawfish 
may be twenty feet long with a five-foot snout equipped with saw- 
like teeth. (Figure 107, A, B, C, D.) 

Holocephali. (Chimeras.) — The sea cat has an operculum or 
gill cover and five claspers developed from its fins. It reaches a 
length of three feet and rarely attacks bathers. (Figure 108). 

Subclass Elasmobranchii. Type of the Group — The Skate.^ 
General External Characteristics. — i. Body flattened dorsiven- 
trally. (The flounder is flattened laterally.) 

2. Pectoral fins broad, fused perfectly with head and trunk. 
Pelvic fins well developed and bilobed, bearing claspers in the male. 

3. Ventral mouth with teeth. 

4. Paired nostrils located ventrally. 

5. Dorsally situated spiracles, originally the first pair of gill 
clefts, communicating with the pharynx. 

6. Five pairs of gill clefts located ventrally. (Laterally in the 
dogfish.) 

7. Ventral anus leading into cloaca. 

8. Two small pouches, one on each side of anus with two ab- 
dominal pores opening into coelome. 

Integument.— The epidermis has several layers of cells and is 
richly supplied with glandular goblet cells. The dermis is studded 
with bony dermal placoid scales or " skin teeth," which are based in 

^ Since it is possible to secure rather small mature skates, many instructors prefer 
to use them instead of the shark. We will therefore describe the skate, but present 
figures to illustrate the nervous system of the dogfish. 



228 



PISCES 




Fig. 105. The angel-shark {Rhina Squat'ind). J, dorsal view; B, view of the 
mouth and nasal barbels. />./., pectoral fin; pv.f., pelvic fin; sp, spiracle. (Courtesy 
of Am. Mus. of Nat. Hist.) 




Fig. 106. Common skate. (Courtesy of N. Y. Zool. Soc.) 



PISCES 



229 





Sting Ray 

Dasyatis centrura ( Mitchill ) 



Butterfly Ray 

Pteroplatea maclura ( Le Sueur) 





Eagle Ray 

Myliohatis freminviUei ( Le Sueur) 



Great Manta 

Manta birostris (Walbaum) 




Torpedo 

Tetronarce occidentaZis 
(Storer) 



Fig. 107. Rays. (Courtesy of Nichols and Breder and the N. Y. Zoological Society.) 



230 



PISCES 



bone, cored with dentin or ivory and tipped with enamel from the 
epidermis. The enamel is inorganic, the cells being replaced by 
lime salts. The dentin contains 34 per cent organic matter and the 
bone is cellular tissue. 



tn.sp 




Fig. 108. Chimaeroid fish. After R. Lull. (Courtesy of The Macmillan Co.) 



There are senso?~y tubes or mucus canals on the ventral surface 
just under the skin. They function for touch and chemical sense, 
having ampullae with sensory cells at the inner ends and pores 
opening to the outside. There are no spines on the ventral surface 
except a few bristly ones in the region of the cloaca. 

Muscular System. — The muscles are segmentally arranged, the 
jaw muscles being well developed. Organs not present in the skate 
are the electric organs, best developed in the teleosts, a South Ameri- 
can eel {Gymnotus) and an African Siluroid {Malapterurus) , but 
also found in the Elasmobranch torpedo ray. In the torpedo they 
lie on each side of the head between the gills and the anterior part 
of the pectoral fin. They are vertical prisms, divided by transverse 
partitions of connective tissue into large number of cells formed 
from metamorphosed muscle fibers. These electropaxes or electric 
plates consist of muscle substances and many nerve endings. Four 
nerves connect them with the electric lobe in the medulla oblongata. 

Skeleton. — The skeleton is cartilaginous with a deposition of 
bone in the jaws and vertebral column. The skull of the skate is 
not ossified: It consists of a large cartilaginous case with brain 
cavity; 2 condyles, 1 large ear capsules, 1 large nasal capsules, a 
long rostrum in front and two fontanelles on the roof. The pectoral 
girdle is a hoop of cartilage attached dorsally to the crest of the 
vertebral plate. The ventral region, the coracoid is separated from 



PISCES 231 

the dorsal, scapular region, by three facets serving as attachments 
for the three basal portions of the pectoral fin, while the supra- 
scapula connects the scapula with the crest of the vertebral plate. 
The pelvic girdle is not attached to the vertebral column. In the 
male the claspers are connected closely with the posterior part of 
the hind limb and have a complex cartilaginous skeleton and an 
associated gland. 

Cavities. — The coelom in the trunk is divided into a pericardial 
cavity, lined vf ith. pericardium consisting of coelomic epithelium and 
connective tissue, while the abdominal cavity is lined with peri- 
toneum. In the dorsal neural cavity is found the central nervous 
system. 

Digestive System. — The mouth has teeth (special development 
of dermal teeth) which are worn away at the outside and renewed 
on the inside. A naso-buccal groove connects the nostrils with the 
buccal cavity, while the spiracles which communicate with the 
buccal cavity ventrally, open dorsally behind the eyes. The tongue 
is reduced or almost entirely absent, in skates but is present in 
sharks. Salivary glands are lacking, but the short broad esophagus 
has mucus glands which lubricate it somewhat. The U-shaped 
stomach (see Figure 109) is divided into cardiac and pyloric regions. 
The sfnall intestine is extremely short and receives the secretions 
from liver and pancreas. The three lobed liver has a large gall 
bladder, leading by the bile duct to the small intestine. The 
pancreas at the end of the duodenum, has its duct opening opposite 
the bile duct. The colon is rather large and has a well developed 
spiral valve, in which the mucous layer of the large intestine is so 
coiled that it increases surface for absorption and retards the passage 

of the food. 

The rectal gland, possibly with an excretory function,^ is at the 
posterior part of the intestine. The spleen, a ductless gland, dark 
red in color, is attached to the stomach by mesentery but has no 
digestive significance. It is functional in blood formation. 

Respiratory System. — The spiracles open dorsally, each con- 
taining a rudimentary gill on the anterior wall supported by a 
spiracular cartilage. Water may enter or leave the mouth. The 
spiracles serve as intakes for the respiratory stream and also as 
spout holes to clear away debris and to keep the eyes clean. ^ 

2 Crawford, J. 1899. On the rectal gland of the Elas-mobranchs. Proc. Roy. 
Soc. Edinburgh, vol. 23, pp. 55-61. 

3 Rand, H. W. 1907. Amer. Nat., vol. 41, p. 285. 



232 



PISCES 



In higher vertebrates the spiracle is used in connection with 
audition and while other gill clefts disappear entirely, it gives rise 
to the tympanic cavity and the Eustachian tube. There are five 
pairs of gill pouches, opening internally to the pharynx and externally 
by gill slits. 



Bile due t — -/- — • 



Gall bladder 

Liver 

■Cordioc stomach 




Spiral valve 



Rectal gland 



Fig. 109. Digestive system of skate. (Drawn by W. J. Moore.) 

Water enters the mouth and passes the interior clefts into the 
branchial pouches, then outward by the exterior clefts. Gill 
pouches are developed from the pharynx and so the respiratory 
epithelium is endodermal. Cartilaginous visceral arches alternate 
with the gill clefts. A gill consists of two hemibranchs or half gills. 
The Dipnoi utilize the gills and the modified swim bladder which 
functions as a lung. 

Circulatory System. — The heart is four-chambered consisting of 
one auricle, one ventricle, with an auriculo-ventricular valve with 
two lips, the sinus venosus, situated dorsally and posteriorly and 



PISCES 



^33 



with numerous valves, which lead into tlie auricle, and the conus 
arteriosus with six valves, which carries the blood anteriorly from 




■Mondfbulor 
•Frontat 

Spirocular 

Bcrsi/or 

£Jff'eTna/ cor-of/d 
■Inferno/ carotid 
— Comrnon carotid 
— Superior coronary 

Hyo 'dean 

•Anterior innominote 

Posterior coronary 

Ventral aorta 

Verfebrol 

Posterior innominate 

Auric le (ofrium) 
■Afferent ttronctiiof 
Nutrient arteries fgil/s) 

■Efferent brancttio/ 
ttypotironchia/ 

Ventricle 

Bracftial 

■Sob-clovian 



Superior mesenteric 



Fig. 1 10. Arterial circulation of skate. (Drawn by W. J. Moore.) 



the heart to the ventral aorta. (Figure no.) In fishes the heart is 
at the anterior end of the coelome. (Figure in.) The walls of 
the ventricle are thick and the walls of the auricle are thin. The 



234 



PISCES 



hearts of all fishes except the Dipnoans contain venous blood only. 
The ventricle forces the blood through the ventral aorta to the 
afferent branchial arteries to the capillaries of the gills, where it 
is oxygenated and thence passes into the efferent branchial arteries 
and into the dorsal aorta, thence throughout the body. 



Juqu/or vein 
Inferior Jutjular vein 



Veins from abdominal woll- 
Cordinal vein — I 

Hemorrhoidal vein — -1 



Ppigosfric vein —■ 

Iliohemorriioidal vein- 
Posterior anastomosis_ 
of cardinal vein 



Femoral vein~~-^—r — 




Bulbus arteriosus 

-Con us arteriosus 

/Auricle 

■Sinus venosus 

Ventricle 

frecavol sinus 

Hepatio sinus 
■ Cardinal vein 

-Brachial vein 



Cardinal sinus 
Spermatic sinus 



Henal portal veiry 

^Factors of renaj portal 
vein from pelvic and 
lumbar regions 

^Branches of renal portal 
vein enterincj l^idney 



Caudal vein 



Fig. III. Venous circulation of skate. (After Parker's Zootomy. Courtesy of Mac- 

millan and Co., Ltd.) 



The renal portal system is well developed in the Elasmobranchs 
but disappears in birds and mammals. In the skate the caudal vein 
brings blood from the tail, dividing in the abdominal cavity to form 
the right and left renal portal veins, which end in afferent renal veins 
supplying the kidneys. The blood leaves the kidneys by the 
posterior cardinal veins which enter the cardinal sinus. 

The hepatic portal vein is formed by the union of veins that bring 
blood from the stomach, intestine, spleen and pancreas. The 
large vessel thus formed passes forwards and enters the liver. Leav- 



PISCES 



^35 



ing the liver the blood enters the sinus venosus by two hepatic 
sinuses, closely apposed. 

Urinogenital System. — The dark red kidneys lie dorsal to the 
vertebral column. Several tubes from each kidney combine to 
form a ureter. The two ureters open into the urogenital sinus. 



— Testis 
Epididymis 




Fig. 112. Urinogenital system of male skate. (Drawn by W. J. Moore.) 



whence the watery products pass out by the cloaca; in the female 
they open into little bladders — the dilated ends of the Wolffian 
ducts — and thence by a common aperture into the cloaca. 

Segmental ducts divide into Wolffian and Miillerian ducts. 
The Wolffian duct becomes in the male the vas deferens; in t\icfe7nale 
it is an unimportant Wolffian duct; the Miillerian duct becomes in 



236 



PISCES 



the/emale the oviduct, in the male it is a mere rudiment. The body- 
cavity rids itself of waste through the abdominal pores. '^ 

In the male, the anterior portion of the kidney persists as the 
epididymis, and its duct becomes the spermiduct. The posterior 
portion, the functional kidney, has its own duct, the ureter. In the 
female no direct connection exists between the reproductive and 
renal organs in the anterior portion. The ureters open in males 
into a median chamber — the urino-genital sinus — which also re- 

OsNum 
— Esophagus 

-Oviduct 

—Mesonephric duct 
-Ovary 

-j — S/?e// gland 



Uterine portion 
of the oviduct 



Kidney 
^Ureters 



Urinary bloddei^ 
Urinary papilla 

Cloaca 

Opening of cloaca^ 
■Abdominal Pore 

Fig. 113. Urlnogenital system of female skate. (Drawn by W. J. Moore.) 

ceives the spermiducts. This communicates with the cloaca by a 
median opening on a papilla — the urino-genital papilla. There is a 
median urinary sinus in females. The ureters open into the sinus 
or directly into the cloaca. The testes are fastened by a fold of 
peritoneum on each side of the cardinal sinus. (Figure 112.) 
Spermatozoa pass from the testes by the vasa efferentia into a tube 

* Smith et al. have shown that the perivisceral fluid escapes through the abdominal 
pores. They also emphasize the secretory capacity of the pericardium and peritoneum 
in Elasmobranchii. (Smith, H., 1929, J. Biol. Chem., vol. 81, no. 2.) 




PISCES 



237 



surrounded anteriorly by the epididymis. The tube of the epi- 
didymis is continued into the vas deferens which is dilated posteriorly 
into the seminal vesicle and adjacent sperm sac. The vasa. de- 
ferentia open into the urogenital sinus. Sperms pass along the 
groove between the claspers of the male. 

The ovaries are anchored by peritoneum on each side of the 
cardinal sinus. The eggs escape into the 
body cavity, and enter the single anterior 
aperture of the two oviducts. (Figure 1 13.) 
The lower portions of the oviducts open 
into the cloaca. Many of the dog fishes 
and sharks are viviparous^ while the skate 
is oviparous^ with a horny purse (Figure 
114) secreted by its oviducal or "shell" 
glands. 

Nervous System. — The brain consists 
of the fused cerebral hemispheres with a 
nervous roof, the optic thalamus or thala- 
mencephalon, with dorsal pineal body, and 
ventral pituitary body and thinly roofed 
third ventricle within; the mid-brain with 
paired optic lobes above, the crura-cerebri 
below, the Aqueduct of Sylvius or iier 
passing below; the cerebellum with its 
anterior and posterior lobes both marked 
by ridges and grooves; and the medulla 
oblongata which has a thin vascular roof, 
and lateral restiform bodies. There are 
ten pairs of cerebral nerves, and many 
paired spinal nerves.^ (Figure 115, Fig- 
ure 116.) 

Sense Organs. — In the Elasmobranch Fig. 114. Egg case of a 
eye, there is no focusing device. The shape skate. (Drawn by Norris 
of the eye and the density of the vitreous Jones.) 
humor aid in keeping the spherical lens close 

to the pupillary opening of the iris. The ears are sacs with three 
pairs of semicircular canals. Within the vestibule are calcareous 

6 Norris, H. W., and Hughes, S. P. The cranial, occipital and anterior spinal 
nerves of the dogfish, Squalus acanthias. Jour. Comp. Neurol., vol. 31, no. 5, pp. 

293-395- 




238 






1 



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O 



I 

U 
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PISCES 



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C3 



1) ^ > O ^ 




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e ^ 



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I 1 1 1 I I I I I I I 1 1 I 



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PISCES 239 

otolithic particles surrounded by a jelly. The nasal sacs are cup- 
like cavities with plaited cells. They serve for sinell only. The 
sensory tubes are best seen on the ventral surface, where they lie 
just under the skin. At their internal ends lie ampullae, con- 
taining sensory cells. At their outer ends there are pores. It is 

r — No sat capsule 
j^-Olfacfory bulb 

Olfactory ^folk 

Olfactory lobe 

Cerebrurn 

■ Tfialamencepbaton 

^—•f Opffc nerve 

• Optic chioa/na 
•Opfic tracf 
-Inferior fobe 
-Pituitary 

-Oculomotor nerve 

• Trochlear nerve 

-ffesfiform body 

^^^/ - TriqemirtQl nerve 

- S^ m^ -^ Abducens nerve 

•■Facial nerve 

•Auditory nerve 

tvledulla oblon<jafa 

Closso pfiarync^eal nerve* 

Spinal cord 



— Pneumo<jastric nerve 



Fig. 116. Ventral view of dogfish brain, showing cerebral nerves. (Drawn by W. J. 

Moore.) 




probable that they are organs partly of touch and partly of 
" chemical sense." The lateral line organs detect vibrations of low 
frequency. The ear, the lateral line, and a pre-auditory sensory 
patch are developed from a thickening of the ectoderm. The 
ectodermal rudiments of the otocyst and the lateral line are in some 
cases continuous at first. Sensory cells in the canals closely 
resemble the sensory cells of the ear. (See p. 259.) 



240 



PISCES 



Subclass Teleostomi. Order 1. Crossopterygii. {Long-finned 
Ganoids.) — Polypterus bichir {Senegalus) (Figure 117) lives in the 
deeper waters of the Nile (Harrington), but does not bury itself in 
the mud like true mudfishes. The air bladder is an accessory- 
respiratory organ. It is connected by a primitive trachea with the 
pharynx and used as a lung. The larva of Polypterus resembles 
amphibian larvae. It has external gills, and utilizes its pectoral 






Fig. 117. Polypterus bichir. Ganoid. /, full length lateral view of 44 cm. 
Polypterus bichir. X i. la, dorsal view of mid-dorsal line of same. X i. /^, 
lateral view of anterior portion of trunk of same, with pectoral fin removed. X i. 
ic, ventral view of anal fins of same. X i. (Courtesy of Amer. Mus. of Nat. Hist.) 



appendages as supports. The median fin is primitive like that of 
the tadpole, but differs in that it has cartilaginous supports or rays. 

Calaniichthys., the other genus of Crossopterygii, has an eel-like 
shape, and lives in small muddy streams in middle western Africa, 
feeding mainly on Crustacea. The Paleozoic Crossopterygii are 
regarded as probable ancestors of the terrestrial vertebrates and the 
present day fishes. 

Order 2. Chondrostei. — This order has a skeleton largely 
cartilaginous, with ganoid scales and a heterocercal tail. 

The paddlefish or spoon-bill {Poly don) lives in the Mississippi 
River and its tributaries. . It may reach a length of six feet and 
weight of one hundred fifty pounds. It is sluggish, feeding on 
mud, shoveled up with its spoon-bill snout, which is equipped with 



PISCES 



241 




Fig. 118. Short-nosed sturgeon. (Nichols 
and Breder. N. Y. Zool. Soc.) 



many tactile and gustatory end organs. A relative of the American 
spoon-bill lives in the waters of China. 

The sturgeon {Acipenser) (Figure 118) has its rostrum prolonged 
into a snout with a transverse row of barbels hanging from the 
ventral surface. The scales 
are large and arranged in five 
longitudinal rows, and have 
keels. The sturgeons are 
found in the Great Lakes, 
and in the Black and Caspian 

seas. Caviar, is made from the eggs of sturgeons, and their flesh 
is also eaten. They reach a size of thirty-two hundred pounds. 

Order 3. Holostei. — Holostei are between the Elasmobranchs 
and the Teleosts, and include Amia and Lepidosteus. They have 
the cartilaginous and bony skeleton, ganoid scales, swim bladder 
and pyloric appendages of the teleosts; and the conus arteriosus and 
spiral valve of the elasmobranchs. The tail is diphycercal. (See p. 

The gar pikes {Lepidosteus) are fresh water fishes, ranging from 
five to ten feet (Alligator gar), and found in North and Central 
America. They have long slender bony snouts with sharp teeth, 
and kill many other fishes. The air bladder serves as a lung when 
the animal comes to the surface to gulp in a fresh supply of air. 
(Figure 119.) 




Fig. 119. Long-nosed gar. (Courtesy of N. Y. Zool. Soc.) 

The bow fin, Amia calva, called the " mudfish " or " fresh water 
dog fish," resembles the true bony fishes. It has, however, a 
continuous dorsal fin, heavy ganoin covered scales and a tail modi- 
fied from the heterocercal to a shape almost homocercal. The air 



242 



PISCES 



bladder is used as a lung. The male guards the nest and later takes 
care of the young for a short time. The embryonic development is 
less like that of a teleost than of an amphibian. (Figure 120.) 

Order 4. Teleostei. (Gr. — complete, — a bone.) — The teleosts 
include most of our common food fishes. The skeleton is ossified. 
Except for one genus, the spiral valve is absent. The stomach has 




Fig. 120. Bowfin, Jmia caha. (From L. A. Fuertes. Courtesy of Slingerland- 

Comstock Publishing Co.) 

pyloric appendages (120 in the cod). The scales are cycloid or 
ctenoid. The gills are comblike and an operculum is always present. 
The swim bladder is usually present though its duct is not always 
open. The eyes are large and lidless. The optic nerves of Teleostei 
cross each other, without interlacing. 

^ The A kaj'inp tarp n {Elopidae), (Figure 121) called the " silver 
king," is much sought by fishermen as it is a gamey fighter. Its 




Fig. 121. Tarpon. (From Goode. U. S. B. F.) 



large silvery scales furnish ganoin for the manufacture of ornaments. 

The salmon {^Salmonidae) is a marine fish spawning in fresh 
water at the age of four or five years. Its long migration to an- 
cestral spawning grounds has puzzled and thrilled scientists for 
many years. (See page 263.) 

The white fish lives in deep water in the winter and migrates to 



PISCES 



243 



the shallows to feed and to spawn. It ranges in weight from three to 
twenty pounds. The lake trout ranges from a few pounds to over 
one hundred pounds in weight. The red spotted brook trout (speckled 
trout) is a shy fish inhabiting clear cold streams and is much sought 
after by fishermen. (Figure 122.) 




Fig. 122. A, lake trout. 5, brook trout. (From L. A. Fuertes. Courtesy of 

Slingerland-Comstock Publishing Co.) 

The bullheads and catfishes {Siluridae) are for the most part fresh 
water fishes. The Mississippi catfish grows to a length of six feet 
and may weigh one hundred pounds. (Figure 123.) 

The saw-toothed piranha is one of the most savage of fishes and 
although it seldom reaches a length of one foot is feared by man and 
attacks fishes and even alligators. Travellers find that the piranha 
will seize one's fingers, trailing over the side of a boat. In catching 
piranhas, copper wire, three strands thick, is used to attach the hook. 

The barracuda of the Eastern coast which sometimes reaches a 
length of six feet, is an important enemy of crustaceans, fish and 
aquatic mammals. It is reputed to attack man, but most of the 
cases reported proved to be the bites of tropical sharks. 



244 



PISCES 



The chubs, horned dace and carp belong to the family Cyprinidae. 
The German carp is a fish introduced to America in 1872, and now 
plentiful. It is not well flavored and is probably injurious to other 
fishes, as well as active in keeping down vegetation ordinarily fed 
upon by ducks. Gold-fish, Cyprinida, bred for centuries by the 
Japanese, have been developed into beautiful forms. 




Fig. 123. Bull head. 



(From L. A. Fuertes. Courtesy of Slingerland-Comstock 
Publishing Co.) 



The suckers {Castastomidae) are fresh-water fishes with long 
protractile mouths. Mullets are relatives. 

The common herring {Clupeidae) is said to be one of the most 
important food fishes. Slight differences in temperature have a 
great influence on the appearance of the shoals of these fish along 
our coast. 

There are six species of cave-fishes {Amblyopsidae) in the sub- 
terranean streams of Missouri, Kentucky and Indiana. They have 
been studied most by Dr. Eigenmann of Indiana University. The 
eyes are reduced. Loeb has found that some fish eggs develop 
without eyes if kept in the dark (Neo-Lamarckism, page 514). 




Fig. 124. Atlantic flying fish. (From Nichols and Breder.) 

T\iQ. flying fishes {Exocoeiidae) (Figure 124) have the power to 
plane along above the surface of the water. As in other fishes the 
tail gives a great initial impetus. It is said that they can " fly " 
two hundred yards. 



PISCES 



245 



The true eels {Anguillidae) are found in fresh and salt water. 
They migrate upstream to the headwaters of fresh water rivers and 
live there until at maturity they pass down to the sea to spawn. 
It is only recently that their habits became fully known. (See page 
264.) 




Fig. 125. A, pike. B, pickerel. C, muskellunge. (Courtesy of Slingerland-Com- 

stock Publishing Co.) 



The pikes {Esocidae) (Figure 125, A^ B, C) include the pickerel, 
Esox lucius, which is a serious enemy of other more important 
food fishes, and also captures frogs and small birds. The muskel- 
lunge {Esox masquinongy) is a hard fighting food fish reaching a 
weight of one hundred pounds and a length of six feet. 

The mummichogs {Poecilidae) include the salt water minnow, 
Fu7idulus hetej-oclitus, which is not only extremely valuable in 
mosquito extermination on the northern salt marshes of the U. S., 
but is of great use in experimental embryology. (Figure 126, A 
and B.) 

The top minnow {Gambusia affinis) is of great Importance in 
the extermination of the larvae of Anopheline mosquitoes. They 



246 



PISCES 



have been utilized in the southern part of the U. S. and, shipped to 
other countries, have successfully attacked the mosquito larvae 
there. Top-minnows must be renewed in many places where winter 
floods carry them away. 




E-Mevirhot 



Fig. 126. J, Fundulus heterocUtus , male. B, Fundulus heteroclitus, female. (F. E. 
Chidester, Bull. 300, N. J. Exp. Sta., 191 6.) 

The sticklebacks {Gasterosteidae) are interesting because of the 
nest building of the male. He entices the female to the nest and 
after she has spawned, he fertilizes the eggs and guards the nest. 
(Figure 127.) 




Fig. 127. Two-spined stickleback. (From Nichols and Breder.) 



Both the pipe fish and the sea horse {Syngnathidae) are peculiar 
in that the male carries the eggs in a ventral brood pouch. (Figure 
128.) Jordan states that the female deposits the eggs on the bottom 
of the sea and that the male transfers them to his brood pouch. 
The sea horse is the only fish with a prehensile tail. 



PISCES 



247 



The sea basses {Setranidae) are mostly marine. The striped 
bass and the black sea-bass are the most prized by fishermen. The 
latter is said to reach a weight of 300 lbs. 

A small fish {Rhodeus amarus) lives in the embryonic state in the 
gill cavities of the mussel ( Unto). 
Thus a fresh-water mussel may 
send out glochidia that attach to 
an adult fish, which at the same 
time sends its embryos to be shel- 
tered by the mussel. 

The smallest fish in the world 
is the Philippine goby {Pandaka 
pygmaea), which is but five-six- 
teenths of an inch long when full 
grown. A slightly larger goby 
{Mistichthys luzonensis) is also 
found in Luzon, P. I. 

The perches {Percidae) include 
the little used yellow perch and 
the pike perch. The latter is con- 
sidered a valuable species and 
propagated by the U. S. Bureau of 
Fisheries. 

The small-mouthed black bass Evolution^ after Doflein, (Courtesy of 
( Centrarchidae) is extremely gamy. The Macmillan Co.) 
The common sunfish or ^^ pumpkin 

seed " is not to be confused with the Hawaiian " sun fish." (Figure 
129, J and B.) 

The porcupine fishes {Diodontidae) are armed with movable 
spines and when alarmed puff their bodies full of air, and float belly 
upward. (Figure 130.) 

The head fish, or " sunfish " of Hawaii, is an odd appearing fish 
(Figure 131), with a skeleton largely cartilaginous and with heavy 
armor. The smooth skin is extremely thick. The body looks as 
though it extended but a short distance beyond the head and lacked 
a tail entirely. Some specimens are said to have reached a weight 
of 2,000 lbs. (Zane Grey's record fish) and a diameter of 8 feet. 

The shark-suckers, or remoras {Echeneididae) (Figure 132), are 
equipped with a modified anterior dorsal fin resembling a rubber 
boot sole. It acts as a sucking disk, enabling the animals to attach 




Fig. 128. Seahorse, male, with 
abdominal pouch. From Lull, Organic 




Fig. 129. ^, large mouth black bass. 5, long-eared sunfish. (Courtesy of Slinger- 

land-Comstock Publishing Co.) 









■ 






1 


^^1 




^^^^T^??^ 

^^^K^^^ 


V 




^^^^Hk#^^ 


IE 




gQ 



Fig. 130. Puffer fish. (Courtesy of Amer. Mus. of Nat. Hist.) 



PISCES 



249 



themselves to sharks and other marine forms. The remoras have 
been used by natives in capturing other fish (Gudger). The goose 
fishy or angler {Lophiidae), is a fish with an enormous mouth and a 
modified first dorsal ray which it uses as a lure. The common 
mackerel^ the Spanish mackerel, and the tuna (called " horse- 
mackerel ") are examples of the family Scombridae. The tuna is 
large, sometimes weighing 150 lbs. 




Fig. 131. Head fish, Mola mola. (Courtesy of Amer. Mus. of Nat. Hist.) 



T\\efla fishes {Pleuronectidae) include the smaller species and the 
large halibut {holibui). The lateral eye of one side moves over to 
the other and the fish lies on its side. Flounders are well pigmented 
and have been utilized in experiments by Sumner and Mast who 
showed that color change will assume the character of the back- 
ground-checkerboard, etc., if the eyes are intact. Blinded, the fish 
cannot change color, to match its environment. (Figure 133.) 

The upper jaw of the swordfish {Xiphiidae) (Figure 134) is 
extended into a formidable weapon. Instances are recorded in 
which a large swordfish (500 lbs.) has penetrated the bottom of a 



250 



PISCES 



heavy whaleboat. The swordfish is one of the finest of the food- 
fishes, but utilized in New England chiefly. The sailfish is another 
odd type. 

The cod, the haddock, and the hake are all important members of 
the family Gadidae. The cod is now especially valuable as a source 
of cod liver oil. This oil has been used as a remedy for growth 
deficiencies for many years, but recently its importance has been 
much emphasized by the " vitamin " enthusiasts. (Figure 135.) 




Fig. 132. Shark suckers. (Courtesy of Amer. Mus. of Nat. Hist.) 

Subclass Dipnoi. (Gr., " two breathing apertures.") — The Imig 
fishes have a heart with the beginnings of a division into two auricles. 
Gill respiration is combined with the use of a modified swim bladder 
which acts as a lung. A posterior naris opens into the mouth cavity. 
They have paired fins and persistent notochord. The Australian 
lung-fish ( Neoceratodus fosteri) feeds on worms, crustaceans and 
mollusks secured from the bottom vegetation. Its single lung is 
utilized when it comes to the surface. It can survive in stagnant 
and polluted water where other fishes perish. (Figure 137.) 



^^2aa^ 




Fig. 133. A, common mackerel. B, bonito. C, Spanish mackerel. D, halibut. 
(From Nichols and Breder. Courtesy of N. Y. Zool. Soc.) 




Fig. 134. Sailfish. Istiophorus gladius. (Courtesy of American Museum of Natural 

History.) 




Fig. 135. A, cod. (From U. S. B. F. Manual.) B, pollock. C, haddock. Nichols 
and Breder. (Courtesy of N. Y. Zool. Soc.) 



252 



PISCES 



The African lung-fishes {Pj-otopterus) feed on worms, crustaceans, 
frogs and insects. They burrow into the mud, secreting a cocoon of 



Anieniof dorsa/ f/'n ri./f ' 

PectorsJ fin-^ 

Nostri/s, 



'Poster/or donsa/ fin 

?' r^i/fin 




JS'c/e' 



A (Ji// coven' ^ ^^^^'-Pe/v/c fin j^ T 

*- -Ifead A Trunk ^ Ta// -^ 



K. S- FLSM CoMttlNMnv V. 



Fig. 136. Yellow perch indexed. (Courtesy of Amer. Mus. of Nat. Hist.) 

slime, and aestivate during the dry season. A slimy covering en- 
closes the animal except for a small aperture through which lung 
breathing is carried on. 




Fig. 137. Australian lung fish, Ceratodus. (Courtesy of Amer. Mus. of Nat. Hist.) 

The South American lungfish {Lepidosiren) is a trifle more 
terrestrial than Protopterus and lives in a deep burrow in the swamp, 
laying eggs in the soil. It takes several gulps of air at a time when 
it comes to the surface of the water. 



PISCES ^^2 

General Consideration of the Fishes 

Locomotion in fishes may be by: Swimming, leaping from the 
water, crawHng or hopping about with the pectoral fins (Angler 
fish and E. Indian Goby); planing on extended pectoral fins (flying 
fishes); or wriggling after rains from one stream or pond to another 
(eel). 

Coloration. — The coloration of fishes is due to the presence In the 
dermic portion of the skin of (a) special pigment containing cells 
(chromatophores), (-^) a peculiar reflecting tissue composed of 
iridocytes. Coloration varies with the species of fishes and may 
vary in the same fish according to background, age, ill-health, and 
emotions. 

Sound Producing Organs. — (a) Stridulation. — The bull head uses 
its preoperculum for stridulation while the gurnard uses its hyoman- 
dibular bone. In the drumming fish, the postclavicles stridulate 
with a grooved area on each cleithrum and the air bladder takes up 
the vibrations. Friction of the upper and lower teeth causes a 
grinding noise in the mackerel. The sunfish makes sounds like 
those of pigs grinding their teeth. 

{b) Expulsion of the air from the swim bladder and mouth 
produces quite noticeable sounds in the eel, the carp and the loach. 
The eel is said to produce a single note, more musical than any 
uttered by other fishes. The air-bladder and its muscles in the 
drum-fish {Poganias chromis) constitute the most powerful sound 
producing apparatus in fishes. 

Respiration. — The rate of breathing varies with the species, the 
minnow and the stickleback breathing 150 times per minute, while 
the blue wrass and the rockling have a respiratory rate of fifteen 
per minute. Skin respiration, vascular caudal fins and larval 
external gills are important, while some fishes use the air bladder or 
develop special accessory organs for aquatic or aerial respiration. 
Many fishes rise to the surface and swallow the air. The air bladder 
is used for respiration In the ganoids and many teleosts, and in the 
" lung fishes." 

Skin. — P/acoid sc3.\es are found in the Elasmobranchs, and while 
they are usually closely set, we find that in the skate they are scat- 
tered. In sharks one can trace the evolution of placold scales Into 

ieefh. 

Ganoid scales are hard plates forming an armor in such forms as 



254 



PISCES 



the gar-pike. The outer surface " ganoin " is extremely hard and 
smooth and readily polished. (Figure 138.) 

Teleostean fishes have two types of scales, cycloid and ctenoid. 
Cycloid scales are circular in shape and overlap. Ctenoid scales are 
rounded but have a serrated comb-like edge that makes them firmer 
in position. Flounders have ctenoid scales on the upper side and 
cycloid scales on the under side. The pipe-fish and the sea horse 

have scales fused into a 
bony armor. Embryonic 
eels have scales, but in 
adults it is impossible to 
see even traces of them 
with the naked eye. 

In some elasmo- 
branchs and t e 1 e o s t s 
from the depths of the 
ocean we find epidermal 
organs modified from 
glands into luminous 
organs or "photophores." 
Some fishes like shad, 
herring, and menhaden 
have in the tela subcu- 
tanea, crystals of guanin, 
which form the base of 
Ctenoid; 3, ganoid; 4, placoid. (From Hertwig- pearl essence. (See page 
Kingsley. Courtesy of Henry Holt & Co.) 1 57-) 

Fish have chromato- 
phores (melanophores) and change color to match their background, 
but when blinded the color changing stops. 

Poison Glands. — When the poisonous secretion produced by 
glands at the bases oi dogfish spines is injected into the lateral line of 
a fish, respiration is accelerated and the animal soon becomes 
lethargic. Eagle rays and sting rays, have barbed serrated spines 
at the base of the tail and the glandular secretion accompanying a 
blow from the tail, undoubtedly adds to the effects produced by the 
irritation. Several teleostean fish including the catfish, have poison 
glands associated with spines on the dorsal fins or in the axillary 
region. 

Blood. — In fishes the blood consists of a nutritive ^\nd, plasjna^ 




Fig. 138^. Scales of fishes. /, cycloid; 2, 



PISCES 



^SS 



in which float red corpuscles and white corpuscles. In the Cyclo- 
stomata (Petromyzon) the red corpuscles are circular, but in the 
true fishes they are usually biconvex, flat, oval, nucleated and with 
hemoglobin, and rich in iron. In the Dipnoi (lung fishes) the red 




£^S^jU*i^^ 



Fig. 1385. Types of tails of fishes. J, diphycercal fin of Polyptertis bichir. 
(Vertebral column and notochord divide the tail into symmetrical dorsal and ventral 
portions.) 5, heterocercal tail of the sturgeon. (As a result of an upward bending 
of the notochord and vertebral column the fin has become asymmetrical, the ventral 
portion much larger than the dorsal.) C, D, homocercal fins, C, of Amia caka; D, of 
Trutta salar. (By a still greater upward bending of the notochord and vertebral 
column the dorsal portion has almost entirely disappeared and the ventral portion 
almost alone forms the fin, externally apparently symmetrical, but in its internal 
structure very asymmetrical.) ch, chorda; a, b, c, cover-plates. (From Hertwig- 
Kingsley. Courtesy of Henry Holt & Co.) 

corpuscles are larger than in most animals (40 mu-mu in diameter) 
being exceeded in size only by the Urodele Amphibians. Leucocytes 
are not plentiful in most fishes, but are more numerous in the 
Dipnoi than in other vertebrates. 

Digestive System. — In the large intestine of the Elasj72obra7ichti 
there is a spiral valve, lacking in the Teleosteii. The small intestine 



256 



PISCES 



is very short, but receives the secretions from well-developed liver 
and pancreas. 

In the Teleosteii, the teeth are premaxillary, vomerine, superior 
pharyngeal, inferior pharyngeal, and mandibular. There are no 
salivary glands, no spiracles and no posterior nares. The pharynx 
is equipped with a fringe of gill rakers (strainers). The small non- 
muscular tongue is supported by the ventral part of the hyoid arch. 

||gg||I^-- Top-pL 

Co/, epi , 

'^^T^.. Oobl. ce/f 




3as. mem. 



Fig. 139. A highly magnified view of a portion of the intestinal epithelium of the 
sea bass, showing several columnar cells and a large goblet cell. The striated 'top- 
plate' is evident, interrupted at the mouth of the goblet cell. Bas.mem., basement 
membrane; CoLepi., columnar epithelium; Gobl.cell, goblet cell; Top-pl., top-plate. 
(Courtesy of I. H. Blake, 7- Morph., vol. 50, Sept. 1930.) 



The gullet is broad and short, and the stomachy curved, is divided 
into cardiac and pyloric regions with pyloric <r^f^^ ranging from six 
in the perch to one hundred and twenty in the cod, and secreting 
pancreatic enzymes. The pancreas is absent, but in a few teleosts, 
pancreatic tissue is combined with the liver. In the goosefish, 
and many other teleosts there are isolated Islands of Langerhans 
in the mesentery that furnish the requisite " insulin." The Toronto 
investigators have extracted it from fishes, and treated diabetes 
successfully. 



PISCES 



m 



All the Cyprinidae lack peptic glands. Babkin and Bowie ^ have 
shown that Fundulus heteroclitus has no stomach, that pepsin and 
HCl are absent and that every phase of digestion takes place in an 
alkaline medium. 




Fig. 1 40. Scorpaenoid fish. (Courtesy of Amer. Mus. of Nat. Hist.) 



Ljonph. — Fishes have small vessels (the lymph capillaries), 
lymph spaces, and lymph sinuses. In the eel a lymph heart in the 
tail communicates with the smaller of the two caudal veins and 
rhythmically pumps lymph into the vein. Lymph consists of 
plasma minus red corpuscles, but normally rich in the white corpus- 
cles with large nuclei called lymphocytes. 

Endocrine Glands. — The thyroid gland in the Elasmobranchs is a 
large compact organ near the anterior end of the ventral aorta. 
In the Teleostomi it is sometimes paired or as in the perch consists 
of diffuse masses of reddish lobules scattered along the afferent 
branchial artery. The thymus gland of the embryo Elasmobranchs 
and Teleosts has a multiple origin, arising from a series of epithelial 
thickenings, one of which is developed at the dorsal extremity of 
each of the gill clefts except the spiracle. The rudiments invaginate 
and fuse. The thymus of the adult Elasmobranchs is paired, the 
organ lying just above the branchial arches. In the Teleostomi, the 
thymus is found at the dorsal extremity of the last branchial arch 
near the mucous membrane of the branchial cavity. The pancreas 
is represented in teleosts by the pyloric appendages, while isolated 

« Babkin, B. P., and Bowie, D. J. 1908. The digestive system and its function 
in Fundulus heteroclitus. Biol. Bull., vol. 54, no. 3, pp. 254-277. 



258 



PISCES 



Islands of Langerhans in the mesentery furnish insulin. (See p. 
156.) 

Elasmobranchs have two structures, the paired suprarenals and 
interrenals. The suprarenals are segmentally arranged bodies 
situated in pairs on the segmented arteries given off from the dorsal 
aorta. The first pair are called axillary hearts. The interrenal is a 
thin, elongated, yellow body with one or two anterior lobes. It 
extends in the median line between the two kidneys or occupies the 
internal portion of the ventral surface of each kidney. In Teleosts 
the suprarenals, varying from two to five in number, are frequently 
found embedded in the kidneys. 

Lymphoid Tissue. — Ordinary lymphatic glands are absent in 
fishes and it is probable that functional lymphoid tissue abounds 
to compensate. The large anterior portion of the mesonephros in 
the Teleostomi, called the head kidney, is almost entirely replaced by 
lyjnphoid tissue, practically no renal structure remaining. It is 
concluded, from the presence of free red corpuscles and oxyhemo- 
globin, that the head kidney performs a blood destroying function. 
The spleen, of course, forms leucocytes and also destroys blood 
corpuscles, devouring worn out reds. Possibly the head kidney 
performs a similar double service. 




Fig. 141. Four-eyed fish, Anableps dovii. (Courtesy of Amer. Mus. of Nat. Hist.) 

Senses. — Fishes vary greatly in their use of the senses. Some 
are predominantly olfactory or gustatory while others depend 
largely upon vision to direct their movements. In all, the tempera- 
ture sense ^ and lateral line sense are of paramount importance. 

Olfaction, Gustation. ( Chemical Sense.) ^ — Fish have a chemical 
sense dependent on free nerve endings; smell, dependent on a highly 
developed distance receptor, the olfactory nerve; and taste, which 

^ Chidester, F. E. 1924. A critical examination of the evidence for physical 
and chemical influences on fish migration. Brit. Jour. Exp. Biol., vol. 1, pp. 79-118. 

* Parker, G.H. 1922, Smell, Taste and Allied Senses in the Vertebrates. J. B. 
Lippincott, Philadelphia, Pa. 



PISCES 259 

is dependent on the taste buds. Fish are extremely sensitive to 
variations in acidity and alkalinity in the water. 

Vision. — Fish are able to change color, adapting themselves to 
the background. When blinded, they are unable to thus adapt 
themselves. Experiments of Lyon showed that fish see the banks of 
streams, and will react to currents of water even if not directly in 
contact with them. 

Tactile and Kinesthetic Senses. — Currents and surface waves are 
apprehended by fish through the general cutaneous nerves for touch. 
In general, fish react to stream pressure, aligning their bodies to 
face the current. 

Lateral Line. — Parker holds that the lateral line nerves serve in 
an auxiliary capacity aiding the general cutaneous nerves in rheo- 
tropic responses. Lateral line organs are stimulated by vibrations 
of low frequency, about six per second. Parker concludes that 
lateral line organs are intermediate in function between the organs 
of touch and the ear^ the latter being sensitive to vibrations of high 
frequency. 

Hearing. — The surface between the air and the water is a screen 
through which little sound passes. Vibrations of the water induced 
by foot-falls on the bank are not to be confused with stimuli affecting 
the sacculus, which Parker believes to be the chief organ of hearing. 
During the recent war Parker, experimenting with cannon fired 
near the surface of the water, found that fish were driven away 
by the concussion. As vibrations of the air were transmitted to 
the water it is difficult to believe that true hearing was evidenced. 

Messmates and Associates. — The small horse mackerels 
( Carangidae) swim in the shelter of large jelly fishes. A small fish 
{Amphiprion) lives inside the large sea anemone {Crambactis) . 
Fierasfery a small fish, lives in the hind-gut of the sea cucumber. 
Another form lives in the mantle cavity of the large sea snail, 
Strombus gigcis. 

Parental Care. — One of the most remarkable instances of paren- 
tal care by the male is that seen in the sea horse and the pipe fish, 
where the eggs are carried in a ventral brood pouch by the male. 
The males of sticklebacks and lump-suckers guard their nests for 
weeks. The butterfish {Pholis gunnellus) coils around its eggs and 
guards them. 

Habitat. — The trout lives in water ranging from 20° C. to 1° C. 
and spawns in October. The common eel of Europe ranges from 



iGo PISCES 

Iceland to the Nile. In studying the fishes of the New Jersey salt 
marshes during the winter the author found that small miyinows dug 
from their burrows and brought into the laboratory in stiff, immobile 
condition would revive in a short time. 

Britton ^ studied the freezing, overwarming and resuscitation of 
the eel, skate, flounder and cod. When the temperature exceeded 
30° C, or went below — 1° C. the fish became immobile and finally 
the heart stopped beating. Resuscitation was readily effected in 
many cases by transferring the fish to water of the normal tempera- 
ture, about 16° C. In one case a skate, Raia laevis, was exposed for 
" sixteen hours in a refrigerator to a temperature as low as — 20° C, 
the whole of the fish being solidly frozen," and on gradual thawing 
the heart beat returned to a slow regular thythm, but the animal 
did not fully recover. At the lower temperatures, 6° C. to 10° C, 
the respiratory action was almost coincident with heart beat. 

Reaction to Temperature Change. — One of the greatest factors 
in the behavior of fishes is their response to temperature change. 
We find that, by means of heat and cold corpuscles in the skin^ fish 
proceed towards warmer or cooler water, and that it is the relative 
temperature that determines their activity. Herring are sensitive 
to very slight temperature changes, according to Shelford and 
Powers (191 5), reacting to differences as small as 0.2° C. It has 
been shown that temperature changes influence the reactions of 
fishes to lights salinity^ Ph and to internal factors such as the de- 
veloping gonads. Unquestionably this sense is the greatest single 
factor that we find influencing the metabolism and behavior of 
fishes. It must even be considered in connection with the instincts 
of the species. 

Electric Organs. — In the Elasmobranchs we find electric organs 
present in the torpedo ray. The electric eel is a Teleost with the 
power to shock the unwary. With but one exception, electric 
organs are composed of metamorphosed muscles and retain their 
original nerve endings. 

Phosphorescent Organs. — The highest development of piscine 
phosphorescent organs is in fishes inhabiting the depths of the sea. 
A luminous organ in the fish is a collection of gland cells usually 
forming the lining of a series of radially arranged tubules in the 
deeper portion of the organ. The luminous organ contains ganglion 

' Britton, S. W. 1924. The effects of extreme temperatures on fishes. Am. Jour, 
of Physiol., vol. 67, no. 2, pp. 411-421. 



PISCES 261 

cells and nerves joining either a spinal or cerebral nerve. Phos- 
phorescent organs are used to see prey, to dazzle and frighten 
enemies and as recognition lights. 

Harvey ^° has studied luminescence in two species of fish {Photo- 
blepharon and Anomalops). In these forms the luminescent organs 
consist of a large number of sets of parallel gland tubes. The 
lumina of the tubes are filled with an emulsion containing granular 
and rodshaped bacteria living in sy?nbiotic relation. 

Adaptation of Fishes to Their Environment. — Fishes have their 
head, body and tail compressed into a curved spindle form which 
offers little resistance to the water. They have a well-developed 
caudal fin used for propulsion; paired pectoral and pelvic ^^^zj- are 
important in executing lateral movements, while their dorsal and 
ventral fins aid in preserving an even keel. Fishes swim, leap, flop 
and plane. The climbing perch moves up tree trunks by small 
hooks on its pectoral fins. The sea robin uses its pectoral fins in 
progressing over the sandy bottom. The mucus secreted by the 
glands of the skin and the fact that the scales overlap, tend to reduce 
friction in swimming. In many forms the swim bladder furnishes a 
means of varying the specific gravity so that the animal can rise or 
sink in the water. Some fishes are provided with sharp spines and 
poison glands for offense and defense. Well-developed organs of 
vision, olfaction and the lateral line sense enable fishes to locate 
food or warn them of danger. 

Economic Importance of Fishes and Their Relatives 

Positive. — Cyclostomes were formerly used as food. 

Elasmobranchs. — Dogfish, sharks and skates are eaten fresh and 
canned. Shark leather, formerly used for " shagreen " spectacle 
cases, and also for polishing wood and other materials, has recently 
been advertised widely by the United States Bureau of Fisheries for 
use in making shoes, handbags and pocketbooks. Attempts have 
also been made to utilize other elasmobranch skins. Shark fins 
have been used as gelatin In China and India. Sharks are also used 
as fertilizer. Shark liver oil has been used as a substitute for cod 
liver oil. A basking shark may produce over a ton of oil. Dogfish 
oil is now purified and used as an insect repellant. The odor is not 
obnoxious to man. 

10 Harvey, E. N. 1920. The Nature of Animal Light. J. B. Lippincott Co., 
Philadelphia. 



262 PISCES 

Teleosts. — Many species of the bony fishes are valued as food. 
Some of the common food fishes are herring, shad, codfish and sal- 
mon. Fish are eaten fresh, smoked, dried, salted, canned whole, or 
flaked, and pickled. Cod, halibut and salmon skins have been 
suggested as a source of leather, but are not in use by civilized man. 
The Alaskan Indians have for many years used salmon skins to 
make shirts and boots. Eel leather has been utilized for pig-tails 
and flail thongs. Some Southern negroes value eel skins as a cure 
for rheumatism. The swim-bladder of the sturgeon and some other 
fish is used to make isinglass and fish-glue. Menhaden are caught 
by the ton and made into oil and fertilizer. 

Pearl essence is secured from herring, alewives, shad and men- 
haden. The California sardine is also a source. Pearl essence is 
securedr-b^y the extraction of the blade-like crystals oi guanin found 
in the epidermis of the fish. The crystals are separated into uniform 
sizes and when mixed with gelatin are used to coat glass beads, 
making imitation pearls. A solution of guanin is also prepared for 
use as nail-gloss. 

Fish meal is secured from fish and fish waste by cooking without 
scorching, and pressing the oil out while the fish is hot. Fish meal 
is used in poultry and stock feed. 

While it will probably never replace cod liver oil, in furnishing 
Vitamins A and D for human consumption, there is no question 
that the vast quantities of salmon liver oil will reduce prices for the 
cheaper grades of fish oil used in cattle feeding. 

Negative. Cyclostomes. — Lampreys attach themselves to the 
bodies of other fish, cut through the body wall and suck out the 
blood and soft parts until the victim dies. Hags parasitize marine 
fishes, entering the body cavity of the host through the hole that 
they cut. 

Elasmobranchs. — The great white shark called the " maneater " 
sometimes reaches a length of forty feet and can cut the body of a 
man in two at one bite. Small dogfish destroy lobsters, crabs, and 
food fishes, and injure nets and other fishing gear to the extent of 
1500,000 per year in Massachusetts. Sting-rays or " stingarees " 
occasionally injure man. Rays and some sharks have poison glands 
at the base of their dorsal fins. The torpedo or electric ray is able 
to give a shock of fifteen volts and temporarily disable a man. 

Teleosts. — Certain of the bony fishes are enemies of man. The 
barracuda, sometimes reaching a length of six feet, is reputed to 



PISCES 263 

attack man. Its flesh, while said to be poisonous, is probably never 
injurious unless ptomaines have been allowed to develop. (See 
page 243.) The saw-toothed piranha has powerful teeth and oc- 
casionally attacks bathers. It is said not to fear the alligator. 
Some of the catfishes have poison glands at the bases of their spines. 

Migration in Fishes. — Fishes apparently seek waters of a certain 
temperature or acidity or salinity which are the optimum for their 
developing eggs and furnish food for themselves and fry. Certain 
races frequent the same streams year after year unless driven away. 

The fresh water fishes in many cases (trout) travel from the 
larger rivers to brooks, where the temperature is cooler, to spawn. 
Suckers have an annual migration very early in the spring. 

Salmon, shad, and sturgeons leave the salt water for fresh water 
to spawn, but spend their life to maturity in feeding in the salt 
water and migrating only from the deep to the shallow, more brack- 
ish water inshore. When they ascend rivers salmon sometimes trav- 
el over 2,000 miles to spawn. Apparently the young salmon return 
to their ancestral spawning grounds whenever possible. Extensive 
scale studies and tagging experiments of American and European in- 
vestigators have proved that many individuals return after two or 
three years to the very region whence they came as newly hatched 
fish. King salmon have averaged forty-two miles a day for a 
journey of 1,500 miles. In the case of the anadramous (up running) 
fishes such as the salmon, it is the belief of many observers that 
their remarkable ability to find their way back to the " parent- 
stream " is inexplicable except as a mysterious instinct. Some 
would hold that the ancient habit of migration to a region once 
inundated by salt water has persisted through the centuries in 
spite of the fact that the land has risen and that the animals must 
now travel long distances in fresh water. Other investigators have 
concluded that the olfactory and chemical senses, oxygen supply, 
tactile and kinesthetic senses, temperature sense and the hormonic 
stimulation of the developing gonads play an important part." 

" Consult Chidester, F. E. 1924. A critical examination of the evidence for 
physical and chemical influences on fish migration. Brit. Jour. Exp. Biol., vol. 2, pp. 
79-118. The author has recently conceived the idea that the iodin-fat balance may 
be concerned in the migrations of fishes. For example, the eel, living in fresh water, 
may migrate down to the salt water in order to secure the optimum iodin necessary 
for it to mature its eggs or sperms. On the other hand, the salmon, and other ana- 
dramous fishes, may find it necessary to migrate from the salt water to the fresh to 
reduce the iodin content sufficiently so that eggs or sperms may develop under 
physiological conditions determined for the race ages before. 



264 PISCES 

In the case of the eeU a catadramous (down running) form in 
which adults from Europe and America seek the same spawning 
grounds, we have the most remarkable case of " homing instinct " 
known in animals. The larvae of two different species find their 
way back to fresh water streams of the proper continent without 
guidance by older fishes. The eel migrates from fresh waters for 
over 2,000 miles into the ocean and the American and the European 
eels have been discovered by Dr. Johannes Schmidt of Copenhagen 
to have a common spawning ground in the West Atlantic Ocean off 
Florida, about equidistant between the Leeward Islands (West 
Indies) and Bermuda. 

The time for maturity is different in the two species of eels and 
the American eel terminates its larval stage in about one year and so 
is not far enough away from the American coast to go to Europe. 
The European eel takes three years to pass through its larval devel- 
opment and thus is near the coast of Europe when it is time for it to 
move up into fresh water. It is believed that when adult eels 
migrate down from fresh water streams where they have lived 
perhaps 20 years, seeking a spawning ground in salt water, they are 
all maturing sexually and have that stimulus in common. Their 
metabolic condition may determine the optimum salinity and tem- 
perature. Eels take from 5 to 20 years to mature their eggs and 
sperms and then they pass down the brooks and rivers to the ocean 
for their last voyage, for they die after spawning. 

Fossil Relatives of Fishes. — The Elasmobranchii arose in the 
Upper Silurian, and were extremely abundant in the Carboniferous. 
The development of a bony skeleton can be traced in the fossil forms. 
Some of the 2inc\&nt' Selachii had dorsal and anterior spines. The 
fossil Holocephali show in their skulls certain similarities to the 
Dipnoi. Rocks of the Devonian Age (Age of Fishes) show spines 
and teeth of the Holocephali. Physostomous Teleosts (those with 
the duct of the swim-bladder open) are said to be the most ancient. 
Herring-like forms appeared in the Jurassic period. Dipnoi, or 
lung fishes of the type now found in Australia (Ceratodus), are very 
ancient, appearing in the Triassic period. The Dipnoi are inter- 
mediate types between Fishes and Amphibians, but not necessarily 
to be considered the " connecting links." 




CHAPTER XVI 

Amphibia 

The familiar amphibia are the toads, frogs, and salamanders. 
As the name indicates, they Hve two Hves, one in the water and the 
other on land. The majority of the amphibia lay their eggs in 
water and the larvae breathe by gills, while the adults breathe by 
lungs. Some adult amphibia have persistent gills, however. 
Amphibia are of considerable economic importance, toads being 
particularly beneficial in capturing insects. 

Classification 

Amphibia. (Gr., " leading a double life.") 

Apoda or Coecilians. (Legless amphibians found in the tropics.) 

Urodela or Caudata. (Salamanders.) 

Anura or Salientia. (Tailless toads and frogs.) 

Characteristics 

1. Skin smooth, moist and devoid of scales. 

2. Limbs penta-dactylic or with five toes. 

3. Skull articulates with the first vertebra by two occipital condyles, 

and is composed of very few bones. 

4. Lungs are present except in a few cases. 

5. Heart has three chambers, a ventricle and two auricles. 

6. Most of the species undergo a metamorphosis, the young living 

in the water and breathing by means of gills. As the lungs 
become functional these gills disappear, except in a few of 
the lower amphibia. 

7. As a rule, the Amphibia are aquatic or semi-aquatic In habits, 

and even when they live far away from the water during 
most of the year, they nearly always go to the water in the 
spring to deposit their eggs. 

8. Amphibians are confined to the torrid and the temperate zones. 

In the temperate zone they hibernate when cold weather 
sets in. 

265 



266 



AMPHIBIA 



Order i. Apoda (Gymnophiona or Coecilians). — In this family 
there are about forty species, placed in seventeen genera, on slight 
grounds, the characters probably having been developed independ- 
ently in various countries. (Figure 142.) The Apoda have no 
limbs or girdles. The eyes are subcutaneous and probably only 
serve as a means of distinguishing light from dark. They burrow in 
the ground feeding on small invertebrates. They have a protrusible 
sensory tentacle between the eyes and nose. Fossil Apoda are 
unknown, as their subterranean life does not favor preservation. 
Some are oviparous and some are viviparous. 




C B 

Fig. 142. Group of Apoda. A, Caecilia, emerging from burrow; B, Ichthyophis 
glutinosus (nat. size), female guarding her eggs, coiled up in hole in the ground; C, a 
nearly ripe embryo, with cutaneous gills, tail-fin, and still a considerable amount of 
yolk. (Redrawn after P. and F. Sarasin.) (trom Newman, Vert. Zool. Courtesy 
of The Macmillan Company.) 

After hatching, when the gills have disappeared, the young of 
Ichthyophis glutinosa (Ceylon, Malay Islands) take to water and 
move about like an eel, coming to the surface occasionally to breathe. 
This form has from 200 to 300 vertebrae. Apoda have apparently 
degenerated from the ancestral amphibians. 

Order 2. Urodela (Gr., visible tail) or Caudata. — The tailed 

amphibia have many vertebrae and are not so pronounced in their 

metamorphosis as the Anura. 

Trunk Tail 

Vertebrae Vertebrae 

Amphiuma dz 35 

Cryptobranchus 20 24 

Necturus 19 29 



AMPHIBIA 267 

The Urodela may retain their gills permanently, lose them per- 
manently, or may have a persistent gill slit. 

Family 1. Amphiumidae. — The hel/ bender {Cryptobranchus 
allegheniensis) is possessed of two vestigial gill clefts, with no gills. 
C. allegheniensis inhabits rivers and streams of North America and 
reaches a length of over two feet. The eggs are fertilized internally, 
as many as four hundred being produced in strings by the female. 
The larvae have gills. Cryptobranchus has four fingers and five 
toes. The skin is excessively slimy, being rich in goblet cells. 

The giant salamander of Japan {Cryptobranchus japonicus 
maximus), between five feet and six feet in length, is found in the 
mountainous regions of Japan and China where it is still feared 
and even worshipped by natives. It has no gill openings and has 
but three branchial vessels (thus resembling Necturus). It is 
situated from 600 to 4,500 feet above sea level, and feeds on fishes, 
amphibia, worms, and insects that it secures from the small streams 
of mountain meadows. It is caught on the hook and eaten by the 
Japanese. 

The " Congo snake ^' or " Congo eel'' {Amphiuma means) is an 
eel-like salamander growing to a length of three feet. It is found in 
the Mississippi rice fields and in swamps and muddy water. It lays 
hard-shelled eggs and the female coils around them to protect. The 
larvae have external gills with legs larger than those of the adult. 

Family 2. Salamandrinae (Salamandridae) . — The crested newt 
{Ti'iton cristatus) is significant on account of its sexual dimorphism. 
The male has a high crest on the head and trunk. The upper 
surface of the head is black and white, while the under parts are 
orange yellow with black spots. The female has no crest and gen- 
erally has a median yellow line on the back. The crested newt is 
found in Central Europe and the British Isles. It is not found in 
Spain nor in Southern France. 

The vermilion spotted newt, Triturus (Diemictylus) vitidescens, 
is interesting on account of its changes in color. It lives in the 
water for the first three years, becoming green with external gills. 
Leaving the water it becomes yellow with vermilion spots. Re- 
turning to the water for the breeding season it again becomes green, 
establishes pharyngeal respiration and lives in perfect aquatic 
adjustment, only to return to the land again, re-establish oral cilia 
and take on the vermilion and yellow of terrestrial life. 

The Alpine salamander {Salat?iandra atra) is a form that produces 



268 AMPHIBIA 

but two young at a birth, and these feed on the other eggs in the 
uterus and metamorphose before birth. It was claimed by Paul 
Kammerer that this type transformed to another species on bringing 
S. atra to the lowlands. 

The spotted or fire salamarjder {Salamandra maculosa) is the 
European species that Kammerer claimed to have duplicated by 
placing S. atra in water. S. maculosa is found in moist places, 
except when it spawns. Then it seeks the water and deposits fifteen 
or more eggs which have been fertilized by a spermatophore dis- 
charged into the water by the male. The young take nine or ten 
months to develop, and live as gilled forms for about four months 
before they metamorphose into the land type. The cutaneous 
poison of the fire salamander is a milky white fluid fatal to small 
mammals and to the cold-blooded animals as well. It is extremely 
painful when applied to mucous surfaces. 

The tiger salamander {Ambystoma tigrinum) is black with yellow 
spots which may extend from blotches to broad stripes and bands. 
It lives on land, but its larval form, once called Axolotl, may remain 
aquatic or transform according to circumstances and individuals. 
The capacity to retain the larval body and become sexually mature is 
called Neoteny and is a most interesting attribute of certain Am- 
phibia. 

Family 3. Oroteidae. {The Mud-Puppies.) — The common 
mud-puppy ( Necturus maculatus) of North America is possessed of 
large fringed external gills. It has small limbs, lidless eyes, and 
lacks maxillary bones. It is of a brownish color, with black spots. 
(Figure 143.) 

The blind cave mud puppy {Proteus anguineus) is found in caves 
of Central Europe. It has a white body, with three pairs of bright 
red gills. When taken from darkness and exposed for a time to the 
light the skin becomes patched with gray and finally a jet-black. 
Typhlomolge rathbuni is a similar form found in the caves of Texas. 

Family 4. Sirenidae. {The Sirens.) — The mud-eel {Siren 
lacertina) is interesting because of its retrograde metamorphosis. 
Cope found that its young lose their external gills and then rede- 
velop them. However, old Sirens can live without gills. 

References on the Urodela 

Bishop, S. C. 1926. Notes on the Habits and Development of the Mud 
Puppy. N. Y. St. Mus. Bull., no. 268. 



AMPHIBIA 



269 



Reese, A. M. 1906. Anatomy of Cryptobranchus allegheniensis. 

Am. Nat., vol. 40, no. 472, pp. 287-326. 
Smith, B. G. 191 2. The embryology of Cryptobranchus allegheniensis, 

including comparison with some other vertebrates. Jour. Morph., 

vol. 23, pp. 61-157. 




Fig. 143. Necturus maculosus. (Courtesy of S. C. Bishop.) 

Order 3. Anura (Salientia. Ecaudata). — The Anura (Gr., not, 
a tail) are highly specialized types, with marked metamorphosis. 
There are over nine hundred species of frogs and toads in this order. 
They have nine to ten vertebrae with the coccyx (urostyle). No 
tail or gills are found in the adult. 

The Surinam toad ( Pipa) lacks a tongue and has a common open- 
ing for the Eustachian tubes. It is a South American form with 
peculiar breeding habits. Its mating is such that the long oviducts 



270 



AMPHIBIA 




l"'iG. I44. Mid-wife toad, Alytes obstet- 
rlciuis. (Courtesy of the Amer. Mus. of 
Nat. Hist.) 



of the female protrude from her body and the eggs pass out to be 
fertilized by the sperms and then are guided forwards so that they 
are spread over the back of the female, where they sink into pockets 
in the skin. Each pocket has a hinged lid which the larva lifts. 

Thej'?;-^ toad {Bomhuiator igneus) has a purplish ventral surface 
with orange yellow patches. When alarmed it throws itself back 
to display the brilliant abdomen, elevating the head and turning the 
legs over the back. B. pachyphus, a poisonous variety, has lemon- 
colored patches. 

The mid-wife toad {Alytres 
obstetric ans) lives in France 
and Switzerland. The eggs 
are externally fertilized and 
the male carries them away 
with him into the water at 
intervals. When they are 
nearly ready to hatch, he re- 
mains in the water to facili- 
tate such development. 
(Figure 144.) 

The spade-foot toad {Pelo- 
bates cult7-ipes) is a toad which digs deep holes in the sand by 
means of a spur on the hind foot. 

The Bufonidae, the true toads, comprise a large family which is 
found on all continents of the globe. Toads possess a rough skin, 
whose irregularities are caused by the large number of poison glands 
contained in it. Their secretion is abundant and the toad is on this 
account not attacked by many animals (see page 300). Bufo 
leyitiginosiis americanus, the common toad of North America, is 
considered to be of great economic importance. Estimates of its 
value as a destroyer of injurious insects vary from ^5.00 to $15.00 
per individual annually. Toads are said to devour plant-eating 
millipeds which secrete hydrocyanic acid. (Figure 145.) 

The tree frogs ( Hylidae) are an extensive and widely distributed 
family, there being over one hundred and fifty species. They have 
the power of changing color from the ordinary green to either grey or 
dark brown. By means of small discs on the tips of their toes they 
are able to climb trees. They are extremely noisy at night when 
they spend most of their time catching insects. One form (Noto- 
tre?/ia) has in the female a fold of skin on the back serving as an egg 



AMPHIBIA 



271 



pouch. In another type {Hyla goeldii) the female carries the eggs 
in a depression on the back. 

The true frogs, Ranidae, are represented by only one genus {Rana) 
in North America. The bull frog {Rana catesbiana — Figure 146) 
is the largest North American species and one of the largest of the 
genus. It reaches a length of from five to eight inches. The color 
of the upper surface is green or olive brown, marked with dark 
spots. Bullfrogs seldom go far from the water. They feed on other 
species of Rana, and even eat ducks and chickens if small. The 




Fig. 145. Toad. (Photo by Newton Miller.) 



writer has found in the stomach of a single large specimen two full- 
grown leopard frogs, packed as neatly as one places shoes in a box. 
^\\& green frog {Rana cla?nitans) (Figure 147) has a greenish color and 
is marked by small irregular black spots. Its length is three inches. 
It lives in or near the water. The -wood frog {Rana sylvatica) is found 
in damp beech woods often far from water. 

The leopard frog (Rana pipiens), formerly called Rana virescens, 
is the most common of all the North American species of Rana. 
Its greenish ground color is marked by large black blotches, edged 
with whitish, The legs are crossed above with black bars. There 
are two irregular rows of black spots down the back and the lower 
side of the pale body. The legs are very long. 

The pickerel frog {Rana palustris) resembles the preceding species. 



272 



AMPHIBIA 



It is brownish in color, with two rows of large brown spots between 
the dermal plicae which are ridges or folds of skin behind the eyes. 
This species is found in the eastern part of the United States. 




Fig. 146. Rana catesbeiana, the bullfrog. (Courtesy of A. A. and A. H. Wright.) 

The Javan flying frogs {Rhacophorus pardalis) have extremely- 
large webbed feet by which they plane from branch to branch. 

Studies made at the Biological Station in Dominica (Caribbean 
Sea) show that a frog {Eleutherodactylus martinicensis), but one 




Fig. 147. Rana clamitans, the green frog, male. (Photo by A. A. and A. H. Wright.) 

inch long at maturity, deposits its eggs in small groups on wet forest 
mould. The eggs are large enough to be mistaken for those of a 
salamander (one-fourth of an inch in diameter). Tadpoles pass 
through the ordinary gilled stage and develop in a short time, with- 



AMPHIBIA 273 

out living in any liquid except that of the egg. (P. G. Howes, Na- 
ture Magazine, July, 1926, vol. 8, pp. 13-15.) 

A Cuban toad {Bufo empusus), called the shell-headed toad or, in 
Spanish, sapo de concha^ lives in a burrow, and c^kz's, itself in, using 
its hard horny head as an operculum. 

A gigantic frog {Rana goliath) , weighing ten pounds and said to be 
" as large as a good sized terrier," is the largest frog known. It 
comes from French West Africa where it is eaten by negroes who 
" consider its thigh bones priceless for purposes of divination " 
(Barbour). 

The smallest known frog {Phyllobates limbatus), one centimeter 
long, was discovered in Cuba in 1910 by Thomas Barbour after 
sixty years had elapsed from the time when the species was originally 
described. 

Anura. Type — Leopard Frog (Rana pipiens).^ External Char- 
acters. — The frog has no neck, its head being united to the trunk. 
The eyes protrude considerably but can be withdrawn into the orbits 
as the eye socket is not separated from the mouth by any of the bones 
of the skull. In the center of the eye is a dark oval opening, the 
pupil, which is surrounded by a brightly colored ring, the iris. 
The eye is covered at times by the eyelids. The upper eyelid is 
capable of but little movement, but the lower lid can be drawn up so 
as to cover nearly the whole eye. The lower eyelid corresponds to 
the lower eyelid of the mammal plus the nictitating membrane, 
which appears to form a dorsal continuation of the lid. Behind the 
eye is a nearly circular area, the tympanic membrane, the covering 
of the drum of the ear. 

Above and behind the snout lie the paired nostrils or external 
nares, guarded by valves which open and close in connection with 
the respiratory movements. The tip of the upper jaw is movable 
and when it is pushed upward the valves of the nostrils become closed 
and prevent the passage of air. Inside the mouth are a pair of 
openings, the internal nares. On the upper side of the head in 
front of the eyes there occurs a small light-colored mark, the brow 
spot, which is the outer portion of a glandular outgrowth of the 
brain, the pineal gland. (See Hatteria, N. Z. Lizard, page 308.) 

The forelegs are short and consist of three divisions, the upper 
arm, forearm and the hand. The hand has four fingers and an 

^The material herewith presented is largely compiled from Holmes, S. J., 1927, 
Biology of the Frog, The Macmillan Co. 



274 AMPHIBIA 

additional rudimentary finger which is easily felt under the skin. 
The two inner fingers contain three joints each and the two outer 
four joints each. The " thumbs " of the male are thickened notice- 
ably. The hind legs are long and well suited for jumping and swim- 
ming but of little service in walking. They are also divided into 
three parts, the thigh, shank, and foot. The foot is well developed 
and has the ankle remarkably elongated. There are five toes and 
the rudiment of a sixth toe called the prehallux^ situated on the 
inner side of the foot. 

The toes increase in length from the first to the fourth. The 
fifth is a little shorter than the third. The first two toes contain 
three joints each, the third and fourth contain four each, and the 
elongated fourth toe has five joints. The webbed hind feet are 
used in swimming. 

The Skin and Its Appendages. — The loose skin consists of the 
cuticle or epidermis and the cutis vera, corium or dermis, and 
contains numerous glands. The epidermis has several layers of 
epithelial cells, the outer ones horny and flat, the middle polygonal, 
and the inner columnar. Each cell has a distinct nucleus. In 
the deeper cells the nucleus is broad, oval and rounded; in the other 
cells it is flattened and thin. The horny layer is usually very thin, 
consisting of one or two layers of flattened cells, but on the back 
and on the under side of the toes it is very thick and rough. Con- 
tractile ^/o^w^w/ cells are also found in the epidermis. Just beneath 
the horny layers are found the goblet cells or mucous cells. These 
are supposed to contain a substance important in connection with 
the process of casting oflF the skin. Toads and frogs are known to 
eat their shed skins. 

Cutis Vera. — The epidermis is attached to the cutis by means of a 
continuous layer of branched cells deeply stained when the ani- 
mals are fed certain foods. Many of these cells are pigmented. 
This layer is seldom flat, but raised into papillae or folds which are 
repeated by the superimposed epidermis. In addition to this layer 
the corium (dermis) has, except in webs and supplemental toes, three 
distinct layers of connective tissue, with much unstriped muscle 
fiber. 

The skin is loose In structure and serves for an important lymph 
space; accordingly the frog is much used in medical studies oi edema. 
The muscle ^^«- of the cutis is unevenly distributed. It is found in 
the back of the dorsal surface of the head and neck and less freely 



AMPHIBIA 



275 



on the dorsal surfaces of the extremities, but not to any extent on 
the abdomen, breast and ventral surface of the extremities, and is 
absent in the feet. 

Pigment of the Skin. — The greater quantity of the pigment cells 
of the skin is found in the cutis. These cells are called Chromato- 
phores. They play an important part in bringing about the well- 
known changes in the coloring of the skin. These cells have been 
found to be supplied by nerve fibers. When the nerve fibers were 
stimulated, the cells were influenced. Blinded, the frog cannot 
change color. 

fVebs and Folds. — On the under side of the toes are little cushions 
or pads. The toes are connected together by a web which makes the 
foot an excellent paddle. Behind the eyes there extend two ridges 
formed by a thickening of the skin. These are the dorso-lateral 
dermal plicae or folds. 

Muscle. — The muscles of the frog retain their vitality for a long 
time after they have been removed from the body, and accordingly 
they are well adapted for physiological experiments, the large 
gastrocnemius or calf muscle of the frog being used a great deal in 
the study of physiological activity. Contraction may be brought 
about by the application of nervous, thermal, chemical, mechanical 
or electrical stimuli. The response to stimulus is very rapid in 
voluntary muscle and is much slower in involuntary muscle. 

Tendon. — Most of the muscles are attached by one or both ends 
to bones. In some cases the attachment is direct, in others by 
means of a tendon which is a band of very tough inelastic connective 
tissue. The outer surface of the muscle is covered by connective 
tissue or fascia which is more or less elastic. The tendons of many 
muscles are formed by a continuation of x\\^ fascia., which becomes 
thicker toward the end of the muscle where it becomes a dense 
fibrous band. 

Digestive System. (Figure 149.) — The function of food is to 
afford energy necessary to carry on the various activities of the 
organism, and to rebuild wastes. In order that food material 
may be built up into the tissues of the body, it must be rendered 
soluble, so that it can pass through the inner lining of the alimentary 
canal into the blood and lymph, and from these fluids through the 
walls of the cells in the different parts of the body. The frog does 
not chew the food taken into the mouth but swallows it down the 



5ub-mandibular muscle 




■Deltoid muscle 
— Pectoral muscle Zd 

-Pectoral muscle 3rd 
Pectoral muscle 4-tt) 



Linea olbo 
External oblique muscle 

Tronsversus muscle 

Myocomma 

— Pectus abdominis muscle 



--Rectus onticus femoris 
Vastus internus 
Triceps extensor femori3 



Adductor moijnus 



Pectus Internus major 
Pectus internus minor 



Ex tensor cruris 

Titjialis onticus 

Tibiolis posticus 

Gastrocnemius 



— Tendon of Achilles 
—Plantar aponeurosis 



B A 

Fig. 148. yf, amphibian muscular system. Ventral view. 5, outside view of the leg. 

(Drawn by G. C. Weber.) 



AMPHIBIA 



277 



esophagus into the stomach where it is acted upon by the gastric 
juice. 

The alimentary canal consists of: {a) the esophagus, a short, 
wide tube leading from the buccal cavity to the mouth; ih) the 
stomachy a wide tubular sac, one and one-half inches long, narrowed 
behind and separated from the duodenum by the pyloric constric- 
tion, a valve; {c) the small irjtestine, with the duodenum., one inch 



/r'/gh/ auricl^ 



ffight ovic/act'~^<^_ \ 



/?/'ghf /arxj - 

Sysf'ema'fic trunks' 
Coel. mes. ortery 
Pt. cv. vein - 

/?, kidney 
f^. oviduct 

Ureter 
Dorsal oorfa—' 
flight oviduct"-' 

Reef urn '' 




Ventricle 

J Left auricle 

Left oviduct 



"^ /^ostcovaj vein 
- Liver 
—Ouilei^ 
—Lett Jung 

--Left oviduct 



'g^^'-Left ovary 

zc'Le'tt oviduct 
"Left oviduct 



Urinary bladder 



/Abdominal vein 

Fig. 149. Organs of a female frog. (From Newman, after Parker and Haswell. 

Courtesy of The Macmillan Co.) 

long, bent back parallel with the stomach, and the coiled ileum^ a 
slender tube about four and one-half inches long; {d) the large 
intestine or rectum^ a straight tube about one and one-fourth inches 
long and three-fourths of an inch wide; (<?) the cloaca^ continuous 
with the large intestine. It receives the large intestine^ bladder^ 
ureters and genital ducts. 

Accessory Organs. — The liver is a reddish brown organ with two 
lobes connected by a narrow bridge. The left lobe is large and 
subdivided into two. The gall bladder is a small spherical greenish 



'/ 



278 AMPHIBIA 

sac between the lobes of the liver. The bile duct leads to the 
duodenum, one-half inch below the pylorus. The distal end reaches 
the pancreas. The pancreas is a whitish irregularly lobed mass lying 
in loop between stomach and duodenum. Pancreatic ducts are 
numerous and open into the bile-duct which passes through the 
pancreas to reach the duodenum. 

Layers of Stomach. — id) Serous, flattened and derived from 
peritoneum; sub-serous, consisting of a few longitudinal muscles and 
connective tissue, {b) Circular muscle layer, {c) Submucous, 
composed of connective tissue and blood vessels with a muscularis 
mucosae made up of inner circular and outer longitudinal muscles. 
{d) Mucous, consisting of glands embedded in a matrix of connective 
tissue. 

At the cardiac end of the stomach, the glands are long and their 
mouths deep. The pyloric glands are less deep with the mouths 
of the glands deeper in proportion. 

Gastric Digestion. — As in higher vertebrates, the gastric juice 
contains HCl and the ferment pepsin and acts on protetlfs, converting 
them into soluble peptones. There is no action on carbohydrates 
and fats. The secretion of the esophagus is alkaline and lubricates 
the esophagus. It must be made acid by the gastric juice before 
it can digest a substance. Holmes states that the pepsin content 
of the esophageal glands of the frog is greater than an equal area of 
the stomach. The frog digests a piece of worm in about twenty- 
four hours. 

The small intestine has folds but no true villi or glands in the 
mucous layer. Goblet cells and absorptive cells are found. The 
small intestine receives the bile and pancreatic juice and is important 
in absorption. The intestinal juice is primarily amylotic. 

Pancreatic secretion is alkaline from Na2C03 and contains three 
ferments: (i) Trypsin, which changes proteins to amino-acids to 
peptones, completing the action of the digestive juices. Unlike 
pepsin it acts in an alkaline or neutral medium. (2) Amylopsin, 
which converts starch to sugar. (3) Steapsin or lipase, which 
splits fats into fatty acids and glycerin and then emulsifies and 
saponifies them. 

The liver secrets bile, an alkaline fluid of complex composition. 
The fatty substance, cholesterin, and the bile pigments are waste 
products. In higher vertebrates it has been proved that bile has a 
weak ferment that acts on fats, aiding in their emulsification. 



AMPHIBIA 279 

It also has slight amylotic Q.n6. proteolytic ferments. Desaturation of 
fats is one of the most important functions of the liver. 

The principal function of the liver is the formation of glycogen, 
sometimes called " animal starch." The glycogen is given out into 
the blood in the form of dextrose, into which it changed by an enzyme 
in the hepatic cells. The liver thus acts as a reservoir for food, 
storing it up when it is in excess, expending it gradually to tide over 
periods of fasting, such as hibernation. Glycogen is also found in 
muscles, ovaries, the central nervous system and the skeleton. 
The pancreas regulates the liberation of sugar (page 455). 

As an organ of excretion the liver collects u7-ea from the muscles 
and so changes it that the kidneys can extract the injurious sub- 
stances more readily. 

When food passes from the stomach into the duodenum of the 
intestine it has an acid reaction due to gastric juice. In the duo- 
denum it is mixed with bile and pancreatic juices which are alkaline 
and so is neutralized. Proteins not acted on by pepsin are acted 
upon by the trypsin of the pancreatic juice and converted into 
peptones. The pancreatic juice changes starch into sugar. The 
soluble food is absorbed through the walls of the intestines into the 
blood and lymph. 

Spleen. — Since the spleen is found attached to the digestive tube 
by mesentery it is usually identified and drawn with the digestive 
system. It is, however, ductless and important in connection with 
the circulatory system, but without digestive function. During 
embryonic life the spleen produces red corpuscles. Even in the 
adult amphibian spleen leucocytes (white blood corpuscles) and 
occasional spindle cells are formed. The destruction of old, worn- 
out, red corpuscles and the ingestion of wastes with pigment 
granules seem to be important splenic functions. 

Circulatory System. — The functions of the circulatory system 
are to carry food material and oxygen to all parts of the body, and 
to remove the CO2 and other waste products of tissue metabolism 
to the organs where they are eliminated. Two fluids, blood and 
lymph, perform these functions. 

The vascular system of the vertebrate is a closed system of tubes 
of vessels filled with blood, and ramifying through all parts of the 
body. Its main parts are: The heart, which contracts and con- 
tinually drives the blood around the system of vessels, the arteries, 
which take the blood from the heart to all parts of the body, the 



28o 



AMPHIBIA 



Carotid arch 
Systemic orcti 

^ci/mocufoneaus orchj 

ffitjtit auricle 
Left auricle 




'External carotid 
-InternoJ carotid 

Carotid qland 
Laryncjeal 



—Great cutaneous 
•-Pulmonory 



Occipifo- 
vertebral 

■Subclavian 
Vertebral 



Celiaco- mesenteric 



■Anterior mesenteric 
■L umt?ors 



■Posterior mesenteric 



//iocs 



Sciatic 



Fig. 150. Arterial system of frog. (Drawn by W. J. Moore.) 



AMPHIBIA 



281 



veins, which carry the blood from these parts back to the heart, 
the capillaries, which are very small vessels connecting the arteries 
and veins. (Figure 151.) 

Structure of the Heart. — The heart of the frog, situated in the 
anterior part of the body cavity ventral to the liver, lies within a sac, 
the pericardium, whose cavity is completely cut off from the coelom. 



£x ternol jugular 
Infernal juqulor 

Left auricle 



Hepafic vein 




Coslric t^e/'n 
HepoliC porfol vein 
Duodena/ vein — 

Jnfesfinol vein - 

Sp/enic vein - 

Ren of vein ^^ 



Renol porfol vein 

Vesical vein , 



Sciotic '/ein — 



Righf auric fe 

-Pre-cavat 

Sinus venosus 

^ — Pulmonary 
Cardiac yein^^^^CfSrochiof vein 

—Lunq 

-Musculofenous 

■L iver 

Abdominal vein 
■PostccivaJ veir) 
■Testis 
Spermafic vein 

- -J /Sidney 

OorjO'/mnbar vein 



— Abdominal vein 



Pelvic vein 



femoral vein 

Fig. 151. Venous system of the frog. Dorsal view. (After Parker and Haswell. 

Courtesy of Macmillan and Co., Ltd.) 

although originally continuous with it in early development. In 
Amphibians and in Reptiles, the heart has three cavities, two auricles 
and one ventricle. 

The venous blood from the body is received into the right auricle 
and the purified blood from the lungs into the lejt. Both throw 
their contents into the ventricle which pumps the mixed blood in 
two directions, partly to the lungs and partly around the system. 



282 



AMPHIBIA 



Circulation Is incomplete, since three kinds of blood are found, 
arterial, venous, and mixed. In many animals arrangements exist 
which nearly separate venous from arterial blood. 

When the pericardium is opened on the ventral side, the following 
parts come into view: (i) The conical ventricle with its apex pointing 
backward. The ventricle has very thick muscular walls and ap- 



Truncus arteriosus 



Ouricle 



flight auricle—— 

3pira/ vo/ve— 
Bulbus cordis 



Dorsaf otric 
venfricuior \fal\/e 



VerttricJe 




Opening into pulmonary vein 
Opening into sinus venosus 

Septum 



Riqht olrio 

ventricular valve 



■Muscle ridges 



Fig. 152. Internal view of the heart of the frog. (Modified from Kerr. Courtesy 

of Macmillan and Co., Ltd.) 



pears paler than the rest. (2) The thin-walled auricles lie imme- 
diately in front of the ventricle; they are separated internally by a 
septum. (3) The truncus arteriosus, a cylindrical body arising 
from the right anterior border of the ventricle, and running obliquely 
across the auricles. It divides into two trunks which soon give rise 
to arteries — common carotid, systemic and pulmoCutaneous. (4) 
The sinus venosus, a thin-walled sac, dorsal to the ventricle and 
behind the auricle; it receives two precavae and the large postcava. 



AMPHIBIA 283 

The four divisions of the heart contract in order, first the sinus 
venosus, then the two auricles, next the ventricle, and lastly the 
truncus arteriosus. (Figure 152.) 

Internal Structure. — The heart propels the blood always in one 
direction and keeps the -pure and impure blood separated. The 
sino-auricular aperture leads from the sinus venosus into the right 
auricle. It is a transversely oval opening, guarded by imperfect 
anterior and posterior valves, in the ventral wall of the sinus venosus 
near the median plane of the anterior end. The right auricle is the 
larger of the two. It has thin walls, thickened by muscular strands 
which form interlacing ridges on its inner surface. In its dorsal 
wall is the opening from the sinus venosus (sino-auricular aperture). 
The left auricle is smaller, sometimes much smaller, than the right 
auricle, which it resembles in the structure of its walls. In its 
dorsal wall, very close to the sino-auricular aperture, is the opening 
of the pulmonary vein. The inter-auricular septmn, the partition 
between the right and left auricles, is much thinner than the walls 
of the auricles, and is placed obliquely, the left auricle lying more 
dorsal than the right. The septum ends with a free posterior edge, 
opposite the auriculo-ventricular aperture. 

The auriculo-ventricular aperture lies at the base of the ven- 
tricle, and rather to the left side. It is guarded by valves which 
hang into the ventricle and it is divided by the lower edge of the 
septum into right and left divisions, admitting blood from the right 
and left auricles respectively. 

The ventricle is conical in shape with the apex backwards, and 
has a small central cavity, with thick spongy walls. The spongy 
character is due to great development of a network of interlacing 
muscle strands similar to those of the auricles. The pockets 
formed by muscle ridges serve to keep the pure and impure blood 
separated. 

Arteries. — The truncus arteriosus., a cylindrical body, arises 
from the right anterior border of the ventricle and runs forward 
across the auricles. (See Figure 150.) It divides in front into a 
right and left branch, each of which again divides into three aortic 
arches, the carotid arch, the systemic arch and the pulmocutaneous 
arch. 

(i) The carotid arch is the most anterior of the three arches. 
It runs around the side of the esophagus and is connected dorsally 
with the second or systemic arch. 



284 



AMPHIBIA 



(2) The systemic arch runs obliquely around the esophagus to 
the dorsal surface and unites with the systemic arch of the other 
side at about the level of the anterior end of the kidneys to form the 
dorsal aorta. 

(3) The pulmocutaneous arch is the most posterior of the three 
aortic arches. It divides into the great cutaneous and the pul- 
monary arteries. 

Veins. — Except the blood coming from the lungs, all of the blood 
is returned to the heart through the three large venous trunks which 
enter the siy2us venosus. The two anterior vena cavae are each formed 
through the junction of three branches, the external jugular, the 
innominate and the subclavian. The posterior vena cava is a median 
vein which returns to the heart the blood from the liver and kidneys 
and indirectly the blood from the other viscera and the hind limbs. 
The three vena cavae open into the sinus venosus. The left auricle 
receives the pulmonary veins. 

Portal Systems. — The blood from the hind limbs does not empty 
directly into the posterior vena cava as in the higher vertebrates, 
but it is forced to pass through a second system of capillaries before 
reaching that vessel. A portal vein, returning blood from the capil- 
laries of some organ, breaks up before reaching the heart into a 
second set of capillaries within some other organ. These again 
unite to form a vein which carries the blood to the heart. In the 
frog there are two portal systems, the i-enal portal system leading to 
the kidneys, while the hepatic portal system brings to the liver blood 
from the hind limbs and from the alimentary canal. 

Action of the Heart. — The auricles contract and the oxygenated 
blood from the left auricle, which has come in from the pulmonary 
vein, is forced into the left side of the ventricle; and the impure 
blood from the right auricle, received from the sinus venosus, passes 
into the right side and middle of the ventricle. 

The blood is prevented from being mixed by being received into 
the before-mentioned pockets or chambers in the ventricle. The 
impure blood, nearer the opening of the truncus arteriosus, passes out 
first and into the pulmocutaneous arches, while the pure pulmonary 
blood from the left side is forced out at the close of the ventricular 
contraction and passes into the carotid and systemic arches. Thus 
the impure blood from the heart goes mainly to the lungs and skin 
where it is purified, while the purer blood passing out towards the 
close of the contraction is sent throughout the body. 



AMPHIBIA 285 

The heart of the frog beats for hours after being removed from 
the body. Electrical, thermal and chemical stimuli will cause the 
heart to beat again after it has ceased normal contractions. 

Vocal Organs. — In vertebrates the vocal and the respiratory- 
organs are intimately associated since the production of sound is 
caused by the expulsion of air from the lungs. The sound-producing 
organs of the frog are situated in the larynx below the pharyngeal 
cavity. The larynx opens into the pharynx through the glottis 
above and posteriorly by a pair of openings into the lungs. The 
skeleton of the larynx is composed of cartilages affording places for 
attachment to muscles which open and close the glottis. 

Sound is produced by the expulsion of air from the lungs which 
set in vibration the paired vocal cords. In the males of many species 
of Rana we find a pair of vocal sacs at the side of the pharynx. 

Respiratory System. — The lungs are thin-walled sacs covered with 
peritoneum. The inner surface of the lungs is divided by septa into 
small chambers or alveoli which increase the amount of surface 
exposed to the air. The walls of the alveoli are richly supplied 
with capillaries. The alveoli are lined with a single layer of thin 
flattened epithelial cells. On the edges of the septa they are colum- 
nar and ciliated. Outside the epithelium is a layer of connective 
tissue containing blood and lymph vessels and highly contractile 
smooth muscle cells. 

The respiratory movements of the frog consist of throat move- 
ments and lung breathing. Throat movements may take place 
without movements of the body or nares, with the glottis closed and 
no air passing into or out of the lungs. Air is drawn through the 
open nares into the mouth cavity. Its floor is lowered, and forced 
out through them when the floor is again raised. Lung breathing 
causes distinct lateral expansions of the body wall. 

The process of respiration consists of: External respiration with 
exchange of gas between the blood and the surrounding medium, 
carbon dioxide being given off and oxygen taken in; and internal 
respiration., gaseous exchange between the blood and the tissues. 
Most of the oxygen in the blood is carried by red corpuscles in weak 
chemical combination with hemoglobin. Oxygenated blood Is 
bright red, impure blood is dark blue in color. 

The skin is a respiratory organ in air and water, and during 
hibernation it is the only respiratory organ. More CO2 is given off 
through the skin than through the lungs. 



286 



AMPHIBIA 



Urinogenital Organs. — Every cell excretes as well as secretes, 
part of the waste passing off as CO2, while solids are discharged by- 
special organs. The skin is an organ of excretion in the frog. In 
higher vertebrates the sweat glands excrete. The liver is an im- 




Suprarenal qlond 
Kidney 



Lcydic^s duct 
S&rninal vesir.l& 
Rectum 



Open'inq of Leydiqs duct 



—Urinary bladder 
(pulled bock) 



Fig. 153. Urinogenital system of male bull-frog. (Drawn by W. J. Moore.) 



portant excretory organ, through bile and the formation of urea. 
The walls of the intestines are important in excretion. The kidneys 
are the most important. The kidneys of the frog are oval, flattened, 
dark red bodies in the posterior part of the body cavity. The duct 
of the kidneys (ureter) is at the outer margin of the kidneys. The 



AMPHIBIA 



287 



-Esophagus 
-Anterior end of oviduct 
^ —Mesentery 




Ureter (Wolffian duct) 



Oviductol opening 
Ureter opening 

Cloaca 

Urinary bladder 



Fig. 154. Urinogenital system of female frog. (Drawn by W. J. Moore.) 




c 

(LI 
> 

C 

o 



I 

u 



§ 

«-» 

u 

u 

CO 



C 

.§ 
o ^-^ 

^ >-' 

^ 8 

c 

^ -^ 

v^ C 
^ 2 

il 

c 

u 

> 

• 

a 
'S 

.2 



r 



1 1 


J 
1 

.5 




>i; 






o 

-T3 



vri 



O 



AMPHIBIA 



289 



ventral surface is flatter than the dorsal. The orange-colored ad- 
renal body, on the ventral surface, is a gland of internal secretion. 
(See page 286.) The kidneys are made up of coiled uriniferous 
tubules with a knot of blood vessels, the glomerulus^ at one end. 

The Wolffian duct is the sperm- 
duct in the male and the ureter 
In the female. The Miillerian 
duct is the oviduct in the female 
and rudimentary in the male of 
Rana pipiens. It is absent in the 
bull frog. The kidneys of the 
male frog are closely related to the 
sexual organs. (Figures 153 and 

154-) 

The vasa eferentia are ducts 
carrying spermatozoa from the 
testes, passing into the substance 
of kidneys and through the kidney 
to the ureter which acts as a vas 
deferens also and is called Ley dig s 
duct. 

The kidney receives blood 
from two sources, the renal ar- 
teries from the aorta and the renal 
portal veins which bring venous 
blood to be purified. The kidney 
secretes urea (NH2CO3) and Na, 
K, Ca, and Mg phosphates and 
chlorides. 

The urinary bladder is a bilobed 
sac attached to the ventral side of 
the cloaca below the openings of 
t\xQ ureters. The bladder collects Fi^- ^S^- Ventral view of the nervous 
11, -11 system or frog. (After Woodruff, Foun- 

urme when the cloaca is closed. , ,. / d- 7 c -c ^ /- 

dations of Biology, from ncker. Lourtesy 

Nervous System.''— i:\i^ brain of The Macmillan Co.) 
(Figure 155, A^ B, andC) consists 

of small olfactory lobes at the anterior end of the two elongated 
cerebral hemispheres; two large optic lobes^ a diencephalon with the 
vestigial pineal stalk attached, a narrow cerebellum situated just 

^ Strong, O. S. 1895. Cranial nerves of amphibia. Jour. Morphol., vol. 10. 




290 



AMPHIBIA 



anterior to the rather wide medulla oblongata. Ventrally one sees 
the paired optic nerves, which cross (optic chiasma), the infundibulum 
to which is attached the pituitary gland or hypophysis. There are 
ten pairs of cerebral nerves. (See table, below.) 

Sense Organs. — Olfactory sense is served by small nasal cavities 
with folded walls of nasal membrane. The anterior nares lead to the 
cavities from the outside and t\\t posterior nares open into the mouth. 
In the fish, as already noted, the olfactory openings were used only 
for smell, but in the amphibia and higher vertebrates, the nares are 
important in respiration. The eyes are well developed, but the 

Origin, Components, Function and Distribution of the Ten Cerebral Nerves 

OF Fishes and Amphibia 



Num- 


Name 


Functional 


Cells of Origin 


Distribution 


ber 




Components 






I. 


Olfactory 


Sensory 


Nasal mucous 
membrane 


Mitral cells of olfactory bulb. 


II. 


Optic 


Sensory 


Gang, cells of 
retina 


Diencephalon (Thalamen- 
cephalon). 


III. 


Oculomotor 


Motor 


III. Nucleus in 
midbrain 


Sup., Inf. and Int. Recti; and 
Inf. oblique muscles of the 
eye. 


IV. 


Patheticus 
or Tro- 
chlearis 


Motor 


IV. Nuc. dorsal 
midbrain 


Sup. oblique muscle. 


V. 


Trigeminal 


Sensory 


(Motor) V. nuc, 


Mandibular nerve to jaws; 






and 


medulla Gass. 


Ophthalmic, Maxillary and 






Motor 


gang. 


Mandibular nerves. 


VI. 


Abducens 


Motor 


VI. Nuc, medulla 


Ext. rectus muscle. 
Sensory fibers associated. 


VII. 


Facial 


Largely 


VII. Side of 


Muscles of face, muscles of hy- 






Motor 


medulla 


oid arch, roof of mouth, pala- 
tine, hyomandibular and 
lateral line (in larval am- 
phibia). 


VIII. 


Auditory 


Sensory 


Side of medulla 


Utriculus, sacculus and semi- 
circular canals of Internal 


IX. 


Glosso- 


Motor and 


Side of medulla 


ear. 
Muscles and sensory corpus- 




pharyngeal 


Sensory 




cles of pharynx and tongue. 


X. 


Pneumo- 


Motor and 


X. Nuc, medulla 


Sensory and motor fibers to 




gastric or 


Sensory 




visceral arches, pharynx. 




Vagus 






heart, and alimentary canal. 



AMPHIBIA 



291 



animal, like many others, is sensitive primarily to moving objects. 
The tongue is supplied v^\t\\ papillae, bearing taste organs. In order 
to detect a substance it must be liquefied. 

Hearing is quite well developed. Near the center of the tym- 
panic membrane is a little protuberance, the tip of the columella, 
the small bone at its inner end connected with an opening in the 
skull which communicates with the inner ear. When the tympanic 
membrane vibrates in response to sound waves, the vibrations com- 
municated to the internal ear produce the sensation of hearing. 

Amphibian tadpoles have functional lateral line organs sensitive 
to vibrations of low frequency, one step below the sensation of 
hearing. In adult amphibia they disappear. In the skin there are 
thermal and tactile organs. 

General Consideration of the Amphibia 

Distribution. — Amphibia live in or near swamps, ponds and 
streams and are never found in salt water. They are on this ac- 
count absent from most oceanic islands. Although many of them 
have lost their gills and taken up terrestrial life, they return to 
water to spawn. The salamanders are for the most part limited to 
the temperate zone, while the Anura are found widely distributed 
and hibernate or aestivate as temperature demands. 

External Anatomy. — There is a great variation in the matter of 
retention of gills in the salamander, some having persistent gills and 
lungs while others lose the gills entirely. 

In the toads and most tree frogs, webs are lacking from the hind 
toes, while certain species of frogs have their toes ending in rounded 
sucking discs. 

Amphibia respire largely by the skin, which is full of capillaries. 
The stratum corneum of the skin is shed periodically. Warts and 
granules are cornifications of the epidermis. In the males of the 
African " hairy frog " {Astylosternus), the granules of the skin are 
developed at the breeding season into hairlike structures, which, 
according to Kingsley, are supplied with nerves and are probably 
sensory in function, although certain writers have described them 
as accessory breathing organs. 

The skin of amphibia is rich in mucus glands, Cryptobranchus 
being especially slimy. Some species of amphibia have well-de- 
veloped poison glands. (See page 300.) 



2g2 



AMPHIBIA 



Skeleton of the Amphibia. — The sku// of the amphibian has less 
cartilage in the adult than is found in the bony fishes. It has two 
occipital condyles for articulation of the first vertebra. The car- 
tilaginous nasal capsules are connected with the auditory capsules 

nasal 

,sphiruhethmoid 

digits 



palaiine- 



fronto-parietaL. 
pterygoid 

cervical vertebra, 
clavicle- 



sacral vertebra 



jTused 




-•calcaneum 



tibio-fibula 

/ 
astragalus 



Fig, 157. Skeleton of garden toad. (After Kellogg, Animals and Man. Courtesy of 

Henry Holt & Co.) 

by trabeculae. In the tailless amphibians {Anura) there is a well- 
developed tympanic cavity opening internally by the Eustachian 
opening. 

In the frog, cartilage develops into the bones of the upper jaw 



AMPHIBIA 293 

and the hyoid apparatus, which remains partly cartilaginous and 
supports the tongue. The cartilaginous cranium has a number of 
cartilage bones and some membrane bones. 

The scapula is ossified and connected with the dorsal supra- 
scapula, which is partly cartilaginous. The ossified coracoid has a 
bar of cartilage, the pro-coracoid, while the clavicle is a membrane 
bone attached to it. The coracoid and pro-coracoid are joined 
ventrally by the epi-coracoid cartilage. 

The episternum, tipped by the cartilage plate, the omosternum, 
projects anteriorly from the united epi-coracoids. The sternum 
extends posteriorly and is tipped by the cartilaginous xiphisternum. 

The pectoral limb consists of the humerus, the fused radio-ulna, 
six carpals and four complete digits with a vestigial pollex on the 
radial side. 

The vertebral column has nine vertebrae and an elongated poste- 
rior urostyle. The vertebral column furnishes a firm dorsal sup- 
porting structure, and protects the delicate nerve cord. 

The pelvic arch consists of two long curved ilia, the fused ischia 
with the ventral fused pubes. Into the acetabulum or socket fits 
the femur. The tibia and fibula are united (tibio-fibula), while the 
two proximal tarsal bones, the calcaneum and the astragalus, are 
extremely elongated, making an additional segment in the hind 
limb. Next to the three distal tarsal bones there are five well- 
developed digits with a spur, the prehallux on the tibial side of the 
first. 

Muscles. — In the lower Urodela the muscles are segmented in 
both trunk and tail. In the Anura, the myotomic structure is for 
the most part lost except in the divisions of the rectus abdominis 
muscles. Muscles are attached to bones by means of bands of 
modified connective tissue known as tendons. 

Physiology. Digestive System. — In the common toad, teeth are 
absent. The retractor bulbi muscles pull the eye balls down in both 
toads and frogs for protection, so that they are able to clamp down 
on worms and insects that otherwise might escape from their mouth. 

When present in the Amphibia, teeth occur on the premaxillae, 
maxillae and vomers, but they are also found on the palatines and 
the dentaries. The tongue is fixed in many salamanders, while in 
the frogs and toads it is usually free posteriorly and can be flipped 
out. In a few forms, called the Aglossa, it is absent. 



294 



AMPHIBIA 



Respiratory System.— The most striking example of metamor- 
phosis occurs in those amphibia in which the larval external and 
internal gills are replaced in the adult by lungs (see Figures 158 and 
159). In many salamanders, respiration is pharyngeal and cuta- 




Infernal carotid 

Hyoid 

—/famus 

cornmun/'cans 

— Oil I cleft 

■Occipifo-vertebral 
— Bulbus arteriosus 
■Scapular 
-Conus arteriosus ^ 



■Pulrnonory 

—Anterior scapular 

-y^ Broc/lio/ 

r^ Fhsterior scapular 

£piijastric 



Pancreot Ic — — 
Hepatic — 

Anterior mesenteric — 



t/roqenifal — C 



liypoqastric 



■Dorsal aorta 
■Gastric 



Coelioco -mesenteric 



—Accessory mesenteric 



^ Posterior mesenteric 



L umbar 

■Posterior epiqosfric 



Iliac 



—Sciatic 



-Caudal 

Fig. 158. Arterial system, ventral view, of Cryptobranchus. (After Reese, Amer. 

Nat., 1906, vol. 40.) 



neous. 



Even in the frog, during hibernation, respiration is cuta- 
neous. The body temperature of the frog varies from 58° to 61,° 
Fahrenheit. Salamanders are mute, but frogs and toads are noisy 
creatures, especially at spawning time. 



AMPHIBIA 



295 



Circulatory System. — It is very easy to see in the embryonic 
Anura and even in the adult Urodela a transition from the fish type 
of vascular system. The red blood corpuscles of the Amphibia are 
oval, nucleated and extremely large. In the salamander Amphiuma, 
the red corpuscles are eight times as large as those of a man. 



i/enfr/c/e 
Superior \/ena co\/a y '^. 

Innominate 1 



Internal Jugular - - 



Brochiol- 



Posterior corc/mol- 



Splenic 




~ — ^ — inferior gastric 

Pancreatic 

Portal 



Atx/ominol 



■Mesenteric 
Inferior cava 

Vein of Jacobson 



Prom urinary ■ 

I Hoc 
Caudal - 
Fig. 159. Venous system. Ventral view. (After Reese, Amer. Nat., 1906, vol. 40.) 



Urinogenital Organs. — In the male amphibian, we find an inter- 
esting condition in that the " Leydig's duct " transports both urine 
and sperm to the cloaca. 

Embryology. — The ripe ova of frogs have distinct po/ar dif- 
ferentiation. The upper " animal pole " is deeply pigmented, while 



296 



AMPHIBIA 



the lower " vegetal pole " has no pigment but is rich in yolk and 
much heavier. Frog eggs are deposited in a mass of jelly which 
encloses green algae aiding in aeration, and which unquestionably 
aids in the absorption and radiation of heat. The jelly also pre- 
serves the eggs from friction and the attacks of enemies. (Figure 
160.) 




Fig. 160. The metamorphosis of the frog. (After Brehm, from Galloway- Welch, 
Textbook of Zoology. Courtesy of P. Blakiston's Son & Co.) 



Cleavage. — The first vertical cleavage occurs about 3 hours after 
fertilization, and divides the ovum into a right and a left half. The 
second vertical cleavage about three-fourths of an hour after the 
first is at right angles to the first while the third cleavage, an equa- 
torial one, divides the dorsal pole from the ventral. Segmentation 
which is total but unequal results in the development of a ball of cells 
of which the dorsal ones are smaller and more numerous than the 
yolk cells beneath. At this stage the egg is called the blastula. 

At the close of segmentation the egg has developed into a hollow 
sphere with the cavity or blastocoel nearer the dark upper pole. 
The upper hemisphere has two quite distinct layers. A crescentic 
groove appears at one side of the egg between the layer of white and 
dark cells. The horns of the crescent extend until they form a cir- 
cle, the blastopore, which is filled with a mass of white cells called the 
yolk plug. Rapid division of the marginal black cells in the dorsal 
region reduces the diameter of the blastopore. At this stage the 



AMPHIBIA 



297 



egg is called the gastrula. The upper germ layer or ectoblast de- 
velops from this layer of black cells. 

From the development of the band of cells and the fusion of its 
right and left halves, a meridional band extends into the dorsal lip 
of the blastopore. On the dorsal side, the groove becomes a long 
narrow slit which is the primitive digestive tract of the frog. The 
roof of the niesenteron, as it is called, is the beginning of the lower 
germ layer, the entoblast. 




Fig. \b\A. Vinal Edwards and Robert Goffin at the nets. Woods Hole, Mass. 



The middle germ layer, the mesoblast^ arises as two plates split 
off from the outer surface of the entoblast and yolk cells. The 
mesoblast separates into two layers with a space between which 
becomes the coelom. 

Germ Layers. — From the ectoblast are derived epidermis, nerv- 
ous system and the lining of the mouth and anus. An anterior 
invagination called the stomodaeum develops into the mouth and 
a posterior one into the proctodaeum. 

From the entoblast are derived the lining epithelium of the diges- 
tive tract and its associated glands. 

From the mesoblast come muscles, bones, blood vessels and urino- 
genital organs. 

Superficial Changes. — At first the egg is spherical, then in four 
or five days it becomes ovoid, finally elongating at about the loth 



298 



AMPHIBIA 



day into a fish-like tadpole with distinct head, body and tail. Three 
pairs o{ external gills ^ which are later to be replaced by internal gills, 

function i n respiration. I n 
front of the two gill-arches 
two depressions unite to form 
a ventral horseshoe-shaped 
sucker. Shortly after hatching 
the mouth and anus are devel- 
oped and the alimentary canal 
becomes tubular and folded 
while its diverticula^ the liver 
and pancreas, are formed. 

Internal gills covered by 
operculi replace the external 
gills. Rapid increase in size 
occurs, the tail which has been 
developed to a remarkable ex- 
tent soon begins to degenerate, 
and the limbs appear. At 
about the 8th week the gills are 
replaced by lungs. At about 
the loth week the tadpole 
ceases to feed on algae, the 
skin is moulted, the gills are 
absorbed, the digestive system 
assumes its adult condition and 
the animal becomes carniv- 
orous. Then the tail is com- 
pletely resorbed, the hind limbs 
Fig. 161 5. George M. Gray, Curator, ^ ^ ■' , , . , 

^.^ ■ D- 1 • t T u . elongate and the animal comes 

Marine Biological Laboratory. «.,njiiga.Lv, m, «_i 

(Photo by Chidester, 1931.) to shore as a young /ro^. 




References 

Hodge, C. F., and Dawson, J. Civic Biology. Ginn and Co. 
Wright, A. H. 1910. The Anura of Ithaca, N. Y. A key to their eggs. 

Biol. Bull., vol. 18, no. 2, pp. 69-71. 
Wright, A. H. 1914. Life Histories of the Anura of Ithaca, N. Y. 

Carnegie Inst. Washington, D. C, Pub. 197. 



AMPHIBIA 299 

Parental Care. — A number of species of frogs and toads build 
nests in which eggs are deposited. Some frogs attach these nests to 
leaves over the water and the tadpoles hatch and drop in. Still 
others deposit their eggs in masses of froth some distance from the 
water. The male sometimes proves to be the caretaker of the young. 
In the obstetric toad he carries strings of eggs until the tadpoles are 
ready to hatch. In another species, the South American Rhino- 
derma, the male transfers the eggs to his huge vocal sacs until they 
are hatched. The viviparous salamanders have already been men- 
tioned. 

Parthenogenesis. — Bataillon, Loeb and others have induced the 
parthenogenetic development of frogs. Parmenter's studies of the 
chromosomes of these fatherless creatures show that they may be 
either male or female. 

Experimental Embryology and Regeneration. — On account of 
the convenience with which amphibian eggs may be secured inland, 
they have been used a great deal in experimental embryology. 
Grafting of two different species and divisions of the egg at the two- 
cell stage have been successfully accomplished. 

W. Roux, Hertwig, Morgan, W. H. Lewis, Spemann, and many 
other investigators have performed experiments on the developing 
eggs of amphibia. Roux injured the first formed blastomeres, 
and Hertwig (1893) and later Morgan (1902) studied the develop- 
ment of half embryos and whole embryos from one of the first two 
blastomeres of the frog's egg. W. H. Lewis first showed (1904, 
Amer. Jour, of Anatomy, vol. 3) that the optic vesicle determines 
location of the lens. Spemann and his students have made many 
significant studies on the development of the eggs of Triton, the 
salamander. (Consult Morgan, T. H., 1927, Experimental Em- 
bryology, Columbia University Press.) 

Harrison, who was the pioneer (see page 495) in tissue culture 
(J. Exp. Z06I., 1907, vol. 4, p. 239; 1910, vol. 9, p. 787), has trained a 
number of anatomists, who have carried on extremely important 
experiments on transplantation and extirpation of limbs and eyes in 
Amphibians. An interesting account of some of the work was 
brought out in the discussion following a lecture by Detweiler given 
at the November, 1930, meeting of the N. Y. Neurological Society, 
and reported in Archives of Neurology and Psychiatry, vol. 25, no. 4, 
pp. 914-919, April 1 93 1. (Consult also papers by Harrison, Det- 
weiler, D. Hooker, F. Swett, and R. Burns.) 



300 AMPHIBIA 

Habitat. — As stated before, amphibia hibernate and aestivate. 
That they are able to live in cavities in solid rock has often been 
reported. But Buckland, after experiments with frogs and toads 
enclosed in cavities of stone and excluded from air and food, found 
that none lived over two years and most succumbed inside of a year. 

Fossil Relatives. — The Stegocephalia are extinct, tailed forms 
which lived in fresh water. Their teeth were complexly infolding 
(Labryinthodonts). One form known as Mastodonsaurus had a 
skull over four feet long and nearly as wide. They were abundant 
in the lower Permian and Upper Pennsylvanian. Traces of gills in 
certain fossil forms indicate that the Stegocephalian larvae were 
aquatic. They were armored, some of them having overlapping 
scales like fishes. 

The Urodela have very few fossil remains. One, found in Ger- 
many, in Miocene rocks, was called " homo diluvii testis," or " the 
man who witnessed the flood." Anuran fossils are rare, and found 
only from the Comanchian to the present, while Apodan {Gymno- 
phionan) fossils are unknown. 

The connecting links between the lobe-finned fishes (Cros- 
sopterygii) and the amphibians have not yet been discovered, but 
comparison of the skulls, labyrinthine teeth and fishlike shoulder 
girdles of land-living amphibia with these fishes indicates their close 
relationship. 

The Stegocephalia are apparently related to certain of the extinct 
Reptiles, the Theromorpha (Therapsida), which appear to have 
affinities with the Mammals. Huxley, comparing amphibians with 
mammals, brought out the fact that both have two occipital condyles, 
and that the carpal bones resemble each other. But Theromorpha 
(see page 331) also have two occipital condyles. 

Economic Importance of Amphibia. Positive. — i. As food, we 
find that frogs (legs) are in considerable demand. 

2. Frogs and toads are important enemies of injurious insects. 

3. As experimental animals for use in Physiology and Embry- 
ology the Amphibia are unexcelled. 

4. Savages secure arrow poison from the skins of some Anura. 
Poisonous Amphibians. — The poisons from the skin glands of 

toads, salamanders and newts, when injected can kill mammals, 
birds, reptiles, and even fishes, provided the dose is proportionate 
to the size of the animal. Small birds and lizards succumb in a few 
minutes while guinea-pigs, rabbits and dogs succumb in an hour. 



AMPHIBIA 301 

A young dog will suffer discomfort for twenty-four hours after taking 
a toad in its mouth. Snakes, however, eat toads without any dis- 
comfort. 

The Indians of Columbia obtain poison from Dendrobates tincto- 
rium by exposing the frog to fire, and use it for shooting monkeys, 
as it acts on the central nervous system. Toads do not cause warts, 
although their skin is poisonous. The Chinese have for thousands 
of years used a toad-skin preparation called " Senso " as a heart 
stimulant. It is said to be fifty to one hundred times as powerful 
as digitalis, to which it is chemically allied. 

Resistance of Amphibia to Poisons. — The toad is not poisoned 
by dosages of digitalis that prove fatal to the frog. This resistance 
depends upon a difference in the tissues, as the isolated hearts be- 
have the same. The frog is tolerant of morphine in quantities fatal 
to man. 

References on the Amphibia 

Barbour, T. 1926. Reptiles and Amphibians. 

Chamberlain, F. M. 1927. Notes on the Edible Frogs of the U. S. 

Report of the Commissioner, U. S. Fish. Com. 
DiCKERsoN, Mary C. 1906. The Frog Book. New York. 
Kirkland, H. a. 1897. The Habits of the American Toad. Hatch 

Expt. Sta. Bull. 46. 
Miller, N. 1909. The American toad. Am. Nat., vol. 43, pp. 641- 

668 and 730-745. 
Surface, H. A. 1913. First Report on the Economic Features of the 

Amphibians of Penna. Zool. Bull., Penna. Dept. Agr., Harrisburg, 

May-July. 
Wright, A. H. 1914. Life Histories of the Anura of Ithaca, N. Y. 

Carnegie Inst. Washington, D. C, Pub. No. 197. 
Wright, A. H. 1920. Frogs, Their Natural History and Utilization. 

Bur. Fish. Doc. No. 888. 



CHAPTER XVII 




Reptilia 

Amnion and Allantois. — Comparison of Reptilia with Aves and 
Mammalia shows that the first two Classes, sometimes grouped as 

Sauropsida^ are much more 
closely related to each 
other than either one is to 
the Mammalia. The three 
classes are alike in possess- 
ing a structure called the 
amnion. 

In the course of devel- 
opment in the reptiles, birds 
and mammals, called 
Amniota, the embryo is 
enclosed in a membranous 
dome-like sac, the amnion, 
which contains a fluid, the 
amniotic liquor. A net- 
work of blood vessels is 
developed over the yolk-sac 
which is an organ of res- 
piration as well as of nutri- 
tion. (Figure 162.) 

w\ '' f / ^^^ I ra^^Mi • vtM* -^" higher mammals, 

however, the allantois 
effects respiration. The 
allantois is a vascular sac- 
like outgrowth from the 
Fig. 162. Vertebrate embryos with their hinder part of the embry- 
membranes. A, reptile or bird; 5, placental onic intestine. It is pres- 
mammal. In A the yolk sac is functional and ent in Amphibia but is very 
the allantois respiratory; in B the yolk sac is 5^1^11. 'XV^ fishes and am- 

functionless and the allantois becomes the , ., . , , • u ^u „ii„„ 
, . , .,■ I J /Ar phibia, lackmg both allan- 

nutntive placenta and umbihcal cord. (Arter ^ , .° 

Wilder, History of the Human Body. Courtesy tois and amnion, are some- 
of Henry Holt & Co.) times called Anamniota. 




302 



REPTILIA 303 

In Amniota, the allantois grows around the embryo as a stalked 
vesicle^ which in reptiles, birds and monotremes lies close beneath the 
egg shell and acts as a respiratory organ during the rest of the em- 
bryonic period. It also receives excretory matters from the kidneys. 
In the mammals above the monotremes, an important vascular 
connection takes place between mother and fetus by means of the 
allantois. This is called the placenta. The allantois becomes 
attached to a definite region of the uterine wall and from it vascular 
processes or villi arise so that the fetal and maternal blood vessels 
come into close relationship with each other. Gills are no longer 
necessary since the allantoic placenta functions in the respiration and 
nutrition of the fetus. 

Classification 

Super-order i. Cotylosauria. Primitive fossil forms. 

Super-order 2. Chelonia. Living forms, including turtles and 
tortoises. 

Super-order 3. Therapsida (Theromorpha) . Fossils linked with 
mammals. 

Super-order 4. Sauropterygia. Fossil forms with a long neck. 

Super-order 5. Ichthyopterygia. Fossil aquatic forms. 

Super-order 6. Archosauria. Besides the primitive fossil Theco- 
dontia, Pterodactyla and Dinosauria, the super-order in- 
cludes one living connecting type, the Rhyncocephalian 
Hatteria, and the living orders of Crocodilia and Squamata. 

Since only four orders of the Reptilia have living representatives, 
we shall discuss these first, and defer the description of fossils to 
the section on Fossil Relatives (page 330). 

Living Orders of Reptilia 

Chelonia. 
Rhyncocephalia. 
Crocodilia. 
Squamata. 

Characteristics 

The reptiles have an amnion, an allantois, a horny skin, ossified 
skeleton, two auricles, two ventricles with incomplete septum 
(except in the Crocodilia), a single occipital condyle, are cold 
blooded, breathe by lungs and have twelve cerebral nerves. 



304 



REPTILIA 



Natural History 

Super-Order 2. Chelonia. — Skull without temporal vacuities. 
Compact body enclosed in a case, consisting of bone and horny 
plates, which form a dorsal carapace and a ventral plastron. The 
vertebrates and ribs of the thoracic region fuse into the carapace, 
and the pectoral and pelvic girdles are internal to the ribs. The 
limbs terminate in claws, or are flipperlike. There are no teeth and 
the quadrate bones are immovable. The cloaca is elongated. 

This order includes tortoises, which are strictly terrestrial; 
turtles y semi-aquatic and marine; and terrapins y which are hard- 
shelled fresh water species. 




Fig. 163. Atlantic green turtle. (Courtesy of N. Y. Zool. Soc.) 



The green turtle ( Chelone mydas) is a marine form, reaching a 
weight of 400 pounds, whose flesh, oil and eggs are all consumed by 
South Americans. In this country, soup and flesh are esteemed 
delicacies. The hawks-bill turtle {Chelonia imbricatd) is a smaller 
marine form once used as a source of tortoise-shell, but now little 
sought. The leathery turtle {Sphargis coriaced) is the largest living 
turtle, reaching a weight of 1,000 pounds and a length of six feet. 
It is marine, but spawns on land. It is inedible. The giant tortoise 
{Testudo) ot the Galapagos Islands is a gentle form, frequently 
photographed at zoos carrying children on its back. It may reach 
a weight of 300 pounds. The common snapping turtle {Chelydra 



REPTILIA 



305 



serpentina) of Eastern America and the alligator snapping turtle 
{Macrochelys lacertind) of Southern United States are vicious forms, 
feeding on fishes. The common snapper attacks young water fowl. 




# 



o 



^ 



® 




e 



^,\ 



® 



o 



c? 



Q 











^ 



Fig. 164. Soft-shelled turtle. (Courtesy of N, Y. Zool. Soc.) 




Fig. 165. Diamond back terrapin. (Courtesy of N. Y. Zool. Soc.) 

The pai?jted terrapin^ Troosts terrapin^ and the yellow-bellied terrapin 
are Httle used for food, but the red-bellied or " slider " terrapin and 
the diamond-backed terrapin are much served in fashionable 



3o6 



REPTILIA 



restaurants. Overfishing has reduced the importance of the terrapin 
fisheries over one half in 30 years. The wood terrapin is edible and 
protected from extermination in New York State. The common 
spotted turtle is said to be unable to eat when out of the water. 




Fig. 166. Skeleton of Cistudo {Emys europaea). V, vertebral (neural) plates; 
C, costal plates; M, marginal plates; Nn, nuchal plate; Py, pygal plate; B, plastron 
(ventral shield); CI, clavicle; Jcl, inter-clavicle; Sc, scapula; Co, coracoid; Pco, acromial 
process (pro-coracoid); Pb, pubis; Js, ischium; Jl, ilium; H, humerus; R, radius; U, 
ulna; Fe, femur; T, tibia; F, fibula. (After Claus-Sedgwick. Sonnenschein, London.) 

The musky map and speckled turtles are all important enemies of 
insects. The common box turtle feeds on insects, but also consumes 
some vegetable matter. It has a lobed plastron which it can close 
tightly. (Figs. 163, 164, 165, 166.) 



REPTILIA 



307 



The soft-shelled turtles {Aspidonectes feros) are edible forms 
found from South Carolina to Texas and up the Mississippi to the 
Great Lakes. They weigh as much as 30 pounds. They are omniv- 
orous, feeding on Crustacea and insects, but also destroying fish 
and waterfowl, since they are extremely fast swimmers. 

Type— The " Slider" Terrapin {Pseudemys rubriventris) .—The 
turtle has no teeth, but horny jaws. Its tongue is broad and soft, 
and the pharynx is thin walled and distensible. The thick-walled 
esophagus bears papillae. The stomach has a pyloric valve. The 
small intestine consists of the duodenu7n, ileum, with an ileocecal 
valve, large intestine and rectum. There are paired cloacal sacs and 
the respiratory system consists of the glottis, larynx, trachea and two 
bronchi. The lungs are large and many branched. The hyoid 
apparatus supports the larynx. Movements of the hyoid, neck 
and anterior limbs aid in respiration. 

Aquatic tortoises and marine turtles have two large sacs at- 
tached to the cloaca. These are filled with water and richly vascular. 
At times, when water is replaced by CO2, they may buoy up the shell 
and supplement the lungs. Females are said to utilize the liquid in 
these sacs in wetting down the eggs deposited in sand on the shore. 

The heart has two auricles and incompletely divided ventricles, 
the septum being perforated. The venous blood passes from the 
postcaval and two precaval veins into the sinus venosus and thence 
to the right auricle. From the right auricle it flows to the right side 
of the ventricle. 

From the right ventricle it goes to the puhnonary artery which 
divides on the right and left; and also through the left aorta which 
sends blood to the viscera and into the dorsal aorta. The left arch 
is therefore venous to the alimentary canal by way of the coeliac. 
Purified blood from the lungs passes to the auricle and left side of 
the left ventricle. The blood then goes through the right aortic arch 
to the dorsal aorta. It is impure, because mixed in the ventricle. 
The turtle has no renal portal, but the usual hepatic portal system. 

Urinogenital Organs. — The urinary system consists of paired, 
reddish, oval kidneys, paired ureters, a urinary bladder shaped like a 
dirigible balloon, the cloaca, oval in shape, and the anus. 

The testes are oval, yellow bodies with vasa deferentia leading 
to the grooved penis which is attached to the anterior wall of the 
cloaca. The paired ovaries are rather diffuse, somewhat resembling 
the single left ovary of the bird. The oviducts open into the cloaca. 



3o8 



REPTILIA 



Turtles lay white oval or rounded eggs in the sand, tamping the 
earth down with the posterior portion of their shell. 

Nervous System. — The cerebral hemispheres and cerebellum are 
large and the olfactory apparatus is well developed. The eyes are 
small and hearing is acute. Tactile sense is well developed, the 
animal being sensitive to raps on its shell. The skin of the ap- 
pendages is especially sensitive. 

Super-Order 6. Archosauria. Rhyncocephalia. — Rhyncoce- 
phalia (Gr. rhynchos, snout; and cephale, the head) are generalized 
types, linking the Squamata, Crocodilia and Dinosauria. They 
resemble the Lacertilia in form, but differ in having a fixed quadrate 
bone. They are represented by one living relative, Sphenodon 
( Hatteria) . (See page 1,1^ i .) 

The New Zealand lizard, Sphenodon or Hatteria, has a well- 
developed ^/«d'«/d'_>'^, sensitive to light. It lives in a burrow. There 
are several fossil relatives from the Permian to the present, with 
maximum development in the Triassic. 




Fig. 167, Gavial. (Courtesy of N. Y. Zool. Soc.) 



REPTILIA 



309 



Order Crocodilia. — Alligators, crocodiles, and caimans, like the 
turtles, have an oval cloacal opening, immovable quadrate bones, 
and bony plates in the skin. They differ in structure from all other 
reptiles although their shape is hzard-like. They have abdominal 
ribs and abdominal sternum. Their teeth are placed in sockets. 
The heart is completely four-chambered. 

The Chinese alligator {Alligator sinensis) lives in the Yang-tse 
Kiang in China. It is a small species, greenish black, with yellow 
spots. It is the nearest living relative of the American alligator. 

The American alligator {Alligator mississippiensis) is found as 
far north as North Carolina. It may reach a length of 16 feet 3 
inches. It is the only crocodilian that bellows. It is much less 
vicious than the crocodiles. Alligators are sold to tourists, and 
there is a constant demand for their hides, used for bags and pocket- 
books. Alligator farms supply animals to the cinema producers. 

The caimans of South America are quite vicious. Gavials, 
found in India, may reach a length of thirty feet, and are quite 
ferocious, but rarely attack man. (Figure 167.) 

The salt water crocodile and the mugger of India and the sacred 
African crocodile ^ are extremely dangerous animals and cause many 
deaths annually. An American crocodile, resembling the African 
form, was found in Florida in 1875, ^1 I^^. W. T. Hornaday. It 
is extremely vicious. 

Order Squamata. {Super-Order F/.)— This order includes two 
sub-orders, Lacertiliay or lizards, and Opkidia, or snakes. The 
Squamata (Lat. squamatus, a scale) have horny scales, renewed 
periodically, movable quadrate bones, a transverse cloacal opening 
and paired penes. 

Sub-Order Lacertilia. (Lat. lacertus, a lizard.) — The lizards, 
chameleons and iguanas have certain characteristics distinguishing 
them from the snakes and the crocodilia. Lacertilia have paired 
appendages or rudiments, scaled ventral surface, tympanic mem- 
branes, a sternum (usually) and movable eyelids. 

The blind-worm, or slow-worm, a limbless lizard {Anguis Jragilis) 
found in Europe and Asia, is a most snaky animal. Its body is 
covered with smooth round scales and its locomotion resembles that 

1 " The crocodile is esteemed sacred by some of the Egyptians, by others he is 
treated as an enemy, and the people of Elephantine even eat their flesh. The 
lonians called the Egyptian ' Champsae ' crocodiles, after the wall-lizards of Ionia." 
(Hereodotus II, 69.) The name Champsae remains today in the Coptic language. 



3IO 



REPTILIA 



of a snake. It is not blind and certainly not at all worm-like. It is 
viviparous. Ditmars cites a case of 2. Jourteen-inch female giving 
birth to sixteen young, each three inches long. Young slow-worms 
feed on termites. Adults feed on earth-worms, insect larvae and 
slugs. The teeth are re-curved and fang-like with traces of a groove^ 
showing that the animal is related to the poisonous lizards. 

The " glass snakes " {Ophisaurus apus of Europe, and 0. ventralis 
of America) are limbless lizards. (Figure 168.) Their movable 
eyelids, and ear openings distinguish them from the true snakes. 
When attacked, they quite easily drop their brittle tail and move 
away to regenerate a new one. 




Fig. 168. Glass snake, Ophisaurus ventralis. (Courtesy of N. Y. Zool. Soc.) 



The beaded lizards ( Helodermatidae) include two poisonous forms 
found in deserts in the United States, Mexico and Central America. 
The Gila monster {H. suspectum), a beaded lizard with grooved 
fangs, has been reported to be quite poisonous to man, but the 
evidence is rather inconclusive. (See p. 328.) Its large tail is a 
reservoir for fat storage. It may reach a length of two feet. 

The geckos of the Mediterranean region {Geckonidae) can run 
on smooth surfaces, climbing walls and ceilings by means of adhesive 
pads on their toes. The suctorial disks are arranged like the slates 
on a roof. The gecko is non-venomous, feeding on insects. It 
drops its tail when attacked. (Figure 169.) 

The European ''green lizard" or wall lizard {Lacerta viridis). 



REPTILIA 311 

is a generalized type. It eats insect larvae but is not able to digest 
those with hard chitinous coverings. Its tail is very brittle and 
quickly dropped off when the animal is irritated. The common 
swift {Sceleporus spinosus undulatus) is an arboreal lizard living 
chiefly on tree-inhabiting insects. It deposits its eggs, which re- 
semble tortoise eggs, in a rather deep tunnel. 




Fig. 169. Ringed gecko, ventral view. Tarentola annularis. Northern Africa. 

(Courtesy of N. Y. Zool. Soc.) 

T\v^ flying dragon {Draco volans) (Figure 170) lives in the Indo- 
Malay region. It has membranes stretched between the fore and 
hind limbs and extends these to plane from tree to tree or limb to 
limb. It is brightly colored like the flowers among which it lives. 

The horned-toad {Phrynosoma cornutum) (Figure 171) is a true 
lizard armed with long neck spines and peculiarly adapted for desert 
life, having a dull grey concealing color and being equipped with 
valves in its nostrils which prevent the inhalation of fine sand. It 
drinks dewdrops and eats insect larvae and ants. Captive speci- 
mens have been observed by Ditmars and others to shoot jets ot 
blood from the eyes a distance of five feet. The animal is not 
poisonous, is easily tamed, and can be " hypnotized " by gently 
stroking its ventral surface. 



312 



REPTILIA 



The skinks include a species (Eumeces quinquelineatus) which 
lives from Massachusetts to Florida and westward to Texas. It 
may reach a length of ten inches. It changes in color in a striking 
manner as age increases. 

The monitor ( Varanus sahator) was for many years considered 
the largest lizard. It is found in Ceylon and the Malay Archipelago. 
It reaches the length of eight feet and is able to swallow a hen's egg 

at one gulp. It is used as 
food. 

The Nile monitor ( Var- 
anus niloticus) digs through 
the rain-softened walls of 
the clay nests of a South 
African termite, and de- 
posits its eggs, ten to thirty 
in number, in the center of 
the nest. The termites re- 
pair the nest, but after 
about ten months the 
young escape from their 
leathery egg shells and, 
aided by the rainy season, 
tunnel out and seek the 
nearest stream. 

The largest living lizard 
{Varanus ko7nodoensis) was 
only recently discovered 
in the hills of Kommodo 
in the Lesser Sunda Is- 
lands. It is said to reach 
a length of ten feet. 

The smallest lizard 
( Lepidoblepharis sanctae- 
mariae) found in eastern 
Panama is about two inches long, weighing less than five grams. 
The sea lizard, an iguana {Amblyrhynchus cristatus), inhabits 
the shores of the Galapagos Islands. It feeds on sea weeds and 
when attacked swims away into the sea. The animals are gregari- 
ous, living in flocks of several hundred. 

The common iguana {Iguana tuberculatd) found in tropical 




Fig. 170. Draco volans (flying lizard). (After 
Hilzheimer.) 



REPTILIA 



3^3 



America is largely herbivorous, but the young individuals feed upon 
insect larvae. Adults will also capture small rodents and young 
birds. The iguana is arboreal and grows to a length of six feet. 
The flesh, tasting much like chicken, is considered a delicacy in 
tropical America. 



.rv 




Fig. 171. Phrynosoma. (Courtesy ot" X. Y. Zool. Soc.) 

The chameleons {Chamaeleon vulgaris) are arboreal forms found 
in the Old World, some in Africa and Arabia, others in India and in 
Spain. The club-shaped tongue, half the length of the body, is 
covered with glutinous material and is used in capturing insects. 
The colors include green, blue, grey, brown, black and yellow. 
Chameleons are able to change their color with extreme rapidity, 
but do not, according to Ditmars, assume the colors of their back- 
ground, as do fishes and amphibia. 

The Aynerican " chameleon " {Anolis carolinensis) is found in 
Southeastern United States. It is not a true chameleon, but 
changes color under changed conditions of light and temperature. 
From ashy grey it will turn to a dull yellow or a vivid green. Its 
food is meal-worms and flies and it drinks dew from leaves. It 
reaches a length of six inches. 

Sub-Order Ophidia} (Gr. ophis, a snake.) — Snakes have a 

1 Much of the material on snakes in this text has been compiled from R. L. Ditmars' 
Reptiles of the World and Reptile Book. Doctor Ditmars has inspected a part of the 
MS. 



314 REPTILIA 

bifid protrusible tongue, frequently fanged, movable, displaceable 
maxillary and palatine bones, numerous vertebrae, movable ribs 
and ventral scutes. They lack tympani. Eustachian tubes, sternum, 
and appendages. Their eyelids are fused. The lungs are asym- 
metrical, some species having a degenerate right and others a de- 
generate left lung. The urinary bladder is absent and the urine, 
chiefly uric acid, as in birds, solidifies in the air. The temperature 
of snakes varies from 68° to 84° Fahrenheit. 

"The limbless serpent can outclimb the monkey, 
Outswim the fish, 
Outleap the zebra, 
Outwrestle the athlete. 
And crush the tiger." 

(Owen.) 

The yellow-headed worm snake {Glauconia albijrons) reaches a 
length of eight inches. It lives in ant hills and is a formidable 
enemy of termites. 

The Boidae {pythons and boas) have vestigial hind legs, a pair 
of strong movable spurs attached to vestiges of the pelvic bones. 
Among the common pythons are the regal python, which may reach 




Fig. 172. West Indian boa. (Courtesy of N. Y. Zool. Soc.) 

a length of thirty feet, and can swallow a small antelope; and the 
smaller Indian python, which is much used in side-shows, as it is 
easily tamed. The Anaconda or water boa is extremely vicious. 
It is viviparous, Ditmars recording one specimen that gave birth 



REPTILIA 



3^S 



to thirty-four young, each one twenty-seven inches in length and an 
inch in diameter. (Figure 172.) 

The common boa {Boa constrictor) reaches a length not greater 
than II feet. It is a native of tropical South America. Easily 
tamed it is used by " snake-charmers," although its smaller size 
renders it less thrilling to audiences, fearful lest they miss the sight 
of a snake tightening its coils on its tamer. Ditmars relates a case 
of a brood of 64 young. Other boas include the vicious Cuban boa, 
the common American rubber boa, and the Indian sand boas. The 




Fig. 173. Thamnophis marciana. (Courtesy of A. G. Ruthven.) 



brown sand boa or two-headed snake {Eryx johnii) has a round 
stumpy tail, sometimes painted with " eyes " by the Hindoos, who 
claim that one end of the animal watches while the other sleeps. 

The sub-family Colubrinae includes the majority of snakes. 
All of this family lack poison glands and hollow fangs. (Figure 
173.) The Eastern ribbon snake is a beautiful reptile, reaching a 
length of 3 feet. It feeds on fishes and amphibians. The garter 
snakes {Eutania) are all prolific viviparous forms, and are beneficial 
for the most part. The water snakes iTropidonotus) are sometimes 
quite vicious but are non-venomous. The brown water snake is the 
largest, reaching a length of 5 feet. An Indian water snake {T. 
macrophthalmus) spreads its neck and was mistakenly brought in 
by the natives when the British first offered a bounty for the hooded 
cobra. The Indian rat snake of the Malay peninsula is protected 
by a fine, as a rat exterminator. It reaches a length of 8 feet. The 
American black snake {Zamenis constrictor) is not a constrictor, 
but holds its prey to the ground under a coil. It destroys small 
rodents, but occasionally eats amphibians and young birds. 

T\it family Colubridae include a number of large snakes killing 



3i6 



REPTILIA 



by constriction and feeding entirely on mammals and birds. They 
are of tremendous importance in destroying injurious rodents. 
The pilot black snake ( Coluber obsoletus) is found from New England 
to Florida and ranges west of the Mississippi. It hibernates with 
the timber rattler. The chicken snakes {^Coluber o. quadrivittatus) 
are feared by poultrymen as enemies of young fowls and as egg 
eaters, but destroy more than enough rodents to pay their way. 

The hog-nosed snake, blowing viper or puff-adder {Heterodon 
platyrrhinus) is a most sinister reptile. When alarmed it flattens 
the anterior portion of its body, hisses, shakes the tail and darts its 
head here and there. It feigns death on some occasions, rolling 
on its back and becoming limp. It will not bite. 

The common king snake or chain snake {Ophibolus getulus) 
ranges from Southern New Jersey to Florida and westward to the 
Pacific coast. Although a deadly enemy of the poisonous snakes of 
America and apparently immune to their venom, Ditmars found 
that when injected with the poison of the Cobra, they died within 
the hour. The king snake is cannibalistic but is extremely fond of 
rodents. A large king snake may be 6 feet long. The animal, 
although such an enemy of other reptiles, is easily tamed by man. 
The milk snake [Ophibolus doliatus) is found in the Northeastern 
states. It frequents barns, hunting for mice, and has been mis- 
takenly thought to rob the dairy, although it has never been caught 
" milking the cows." The ring-necked snake (Diadophis regalis) 
found west of Illinois is the largest of the genus. It lays eggs which 
are so thin skinned that they hatch in half the time required by 
other snake eggs. It lives under flat stones and in dead trees and 
feeds upon earthworms, salamanders, young lizards and snakes. 
The scarlet king snake ( Cemophora coccinea) is found in the south- 
eastern part of the United States. Its chief interest is that it is 
confused with the deadly coral snake. The scarlet snake feeds on 
mice and reptiles. It is oviparous and coils around its eggs until 
they are hatched. 

The Opisthoglypha are not as poisonous as the Elapine and Vi- 
perine snakes, since they have furrowed or grooved fangs, located 
at the extreme rearof the upper jaw. Ditmars, however, emphasizes 
the fact that their venom acts on the nerves and that it will kill a 
lizard more quickly than the bite of a viper. 

The annulated snake {Sibon septentrionalis) of Africa and the 
tropical Americas, and the pike-headed snake {Oxybelis acuminatus) 



REPTILIA 



317 



of Mexico and South America, are opisthoglyphs that feed on lizards. 
The Proteroglypha include two sub-families, the Hydrophinae 
which are marine forms, and the Elapinae which include Old World 
Cobras and the New World coral snakes Their fangs are hollow 
and connected with venom glands secreting powerful poison. The 
fangs are rigidly attached on the anterior portion of the upper jaw 
instead of folding back against the roof of the mouth as in the 
viperine snakes. 





^^^y ' ^Bf j^K^^^^Ki^^iiflBlk 






^i^^_ ^^^Bf 




■ 


^^-. jP 


.4 ^ 


' ' . L ■• 



Fig, 174, Sea snake, (Courtesy of N. Y. Zool. Soc.) 

One of the Hydrophinae^ the yellow-bellied sea snake {Hydrus 
platurus), is found in salt water off the coast of Central and tropical 
South America, The sea snakes swim in schools of 20 or more. 
They are preyed upon by fish and sea birds. Their venom is ex- 
tremely powerful and produces a benumbing of the nerve centers. 
(Figure 174.) 

The Elapine snakes have a slender body and a narrow head. 
Their fangs are short, always erect and situated on the anterior 
portion of the jaw. But one genus of these reptiles is found In 
America. 

The Spectacled Cobra or " Cobra-de-Capello " ( Naja tripudians) 
Is found In India and the Malay Archipelago. Although the fangs 



3^8 



REPTILIA 



are extremely small, their wounds are more quickly fatal than those 
of the vipers with large teeth. Spectacled cobras are said to be 
most vicious when in captivity, apparently proving untamable. 
Ditmars states that cobra venom ejected and entering the eyes 
will produce blindness or death. Cobras feed on small rodents, 
birds and amphibians and can swallow eggs entire. They reach a 
length of over 6 feet. (Figure 175.) 




Fig. 175. Asp. (Courtesy of X. Y. Zool. Soc.) 



The Egyptian cobra or Asp ( Naja haje) is a smaller snake than 
the spectacled cobra, reaching a length of not more than five feet. 
It is extremely intelligent and startlingly quick in its movements. 

The king cobra or Hamadryas ( Naja bungarus) reaches the 
length of 12 feet. It is said to be the most deadly of the Old World 



REPTILIA 



319 



snakes. Apparently tamable, it Is most treacherous. Cobras are 
oviparous. In 1927, there were 19,069 deaths from snake-bite in 
India. Cobras and kraits were chiefly responsible. 

The Ringhals {Sepedon hue 7n achates), a South African cobra, 
reaches a length of five feet. It feeds on amphibians, birds and 
their eggs, and small rodents. It ejects jets of poison six feet. 
The krait {Bungarus coeruleus) is an extremely dangerous snake 
found in Asia and the Malay Archipelago. It has no hood. It 
reaches a length of 4 feet. 

The Australian black snake {Pseudechis porphyriacus), an ex- 
tremely venomous snake, is sometimes called the purple death 
adder. (See p. 328, Snake Venoms.) 




Fig. 176. Body rings of false coral snake and true coral snake. (Courtesy of Anti- 

venin Institute of America.) 



Several species of Doliophis are found in Southeastern Asia. 
The venom-secreting glands are not confined to the head but extend 
through the anterior one-third of the body. Due to this strange 
variation, the heart is located more posteriorly than in other snakes. 

About 26 species of the New World Elapine snakes are known, 
two of them being found in Southern United States. The two 



320 REPTILIA 

species of Elaps found in the United States resemble harmless 
forms including the Western milk snake and the scarlet king snake. 

The poisonous snake (Figure 176) has single black rings bordered 
with a pair of yellow rings while in the harmless species the yellow 
rings are single bordered with a pair of black rings. The harlequin 
snake or coral snake {Elaps fulvius) is found in our Southern States 
and ranges into Mexico. It is cannibalistic but very fond of lizards, 
which seem quite susceptible to its poison. Coral snakes seem quite 
gentle and do not " strike " but certainly do bite and chew vigor- 
ously. They are oviparous and according to Ditmars the eggs re- 
quire as much as thirteen weeks for development. 

Family Viperidae. — The viperine snakes are long fanged with 
small vertical movable maxillaries each bearing an extremely long 
hollow fang. Each maxillary has a lever bone aiding in the eleva- 
tion of the fang. When the jaws are closed, the fangs of the vipers 
fold against the roof of the mouth. The majority of the viperine 
snakes have thick bodies and flattened heads, the pupils resembling 
those of a cat eye. 

Certain of the true vipers {Sub-family Viperinae) are horrific 
in appearance while others found in South Africa are according to 
Ditmars " Moderately slender with an ordinary head while the eye 
has a round pupil and there is a loreal plate (between the eye and 
the nostril) as seen in the typical harmless snakes." 

The Cape viper {Causus rhombeatus) has relatively small fangs 
which are lifted at will. Cape vipers are found in Southern Africa, 
reaching a length of about 3 feet. Unlike vipers in general, this 
form is oviparous. It feeds on frogs, apparently without using its 
poison fangs. The common viper ( Vipera berus) is found all over 
Europe and is the only poisonous snake found in the British Isles. 
It feeds on rodents and young birds. The sand natter ( Vipera 
ammodytes) is found in Southeastern Europe. A soft horn about 
one-eighth of an inch in length protrudes from its snout. It 
reaches a length of two feet and is extremely dangerous. It feeds 
on small rodents. 

The Daboia or Russell's viper ( Vipera russellii) is one of the 
most deadly snakes of India. The Puff adder {Bitis arietans), 
found in Africa, hisses loudly at each breath. The gaboon viper 
{Bitis gabonicd) of tropical Africa will stand its ground when sur- 
prised, hissing viciously. Ditmars calls it " the most sinister of all 
the venomous snakes, in its aspect." The horned viper or asp 



REPTILIA 



321 



{Cerastes cornutus) is a small African desert species with a sharp 
spine above each eye. 

The pit vipers {Sub-family Crotalinae) have a deep pit between 
the eye and the nostril. (Figure 177, A and B.) 

The water moccasin or cotton-mouth snake {Agkistrodon piscivorus) 
is a semi-aquatic form found in the Southeastern United States. 




Poison qlond 



Head of Micrurus 

(Pro feroglypha) 





Cross section 
of cjrooved fonq. 

Grooved foncj. 



Poison gland 




Head of Crotalus 

(So ten o q hyp ho) 





Cross section 
of hol/Ov^ fonq- 



Tronsporenf" yiev</ 



of hollov^ fane 



Fig. 177. Fangs and head of coral snake {Micriirus) and rattler {Crotalus). (Cour- 
tesy of Antivenin Institute of America.) 



It reaches a length of six feet. It is omnivorous, devouring fishes, 
amphibians, other^reptiles and small birds and mammals. Death 
may ensue in one-half hour after the bite of an adult specimen. 
(Figure 178.) 

The copperhead snake {Agkistrodon co7ttortrix) is found east of 
the Mississippi River, ranging South from Massachusetts. It 
occurs as far west as Texas. It is not extremely vicious although 
one of the most venomous of forms. Its food includes amphibians, 
small birds, and rodents. It is viviparous and produces as many as 
a dozen young at a birth. (Figure 179.) 

The bushmaster {Lachesis mutus) is found in Central and tropical 
South America. Reaching a length of ten feet, it is said to be the 



322 



REPTILIA 



only Crotaline snake that lays eggs. Ditmars cites a case of death 
in less than ten minutes after an eight-foot bushmaster had bitten a 



man. 







Fig. 178. Cotton mouth (water) moccasin, Agkistrodon piscivorus. (Courtesy of 

Antivenin Institute of America.) 

The. Jer-de- Lance {Lachesis lanceolatus) Is found ranging from 
Southern Mexico into South America. On the Islands of Martinique 
and Guadeloupe it is much feared by workers on sugar plantations. 

In Honduras, the " barba amarilla " or yellow beard, an ally of 




Fig. 179. Copperhead snake, Agkistrodon mokasen. (Courtesy of Antivenin Institute 

of America.) 



REPTILIA 



3^3 



the fer-de-lance of Martinique and the jararaca of tropical South 
America, is feared on account of its size (8>^ feet) and the fact that 
it injects a teaspoonful of poison. (Figure i8o.) 

The diamond back rattlesnake ( Crotalus adamanteus) , found in the 
Southeastern part of the United States, grows to a length of eight 
feet and weighs more than any other Doisonous form. Death ensues 
in less than an hour after its bite. 



■.^\-- 




M^I^Mi?^-^ 



Fig. 1 80. Barba amarilla. (Courtesy of N. Y. Zool. Soc.) 



Other rattlesnakes of the United States include the pigyny or 
ground rattlesnake of Southeastern United States, the Massasagua of 
the Central and Western states, the Texas rattler (6 feet long) (Figure 
181), the timber rattler of the eastern mountains, and the horned rattler 
or sidewinder of the Western states. (Figure 182.) 

Ditmars has recently described a ten-foot Honduran rattlesnake 
that produces paralysis of the neck muscles in a few minutes. 

The smallest adult snake, a Syrian Leptotyphlops, is blind, lives 
in the sand and resembles in size and shape a steel knitting needle. 

General Consideration of Reptilia 

Distribution. — The Lacertilia are of wide distribution. The 
wall lizard {Lacerta muralis) is found from Belgium to North Africa. 
The Chelonia are found in the temperate and tropical regions for 
the most part. The sea-turtles are confined chiefly to the tropical 
seas. The Caimans are found in Central and South America, while 



3^4 



REPTILIA 




REPTILIA 2^^ 

the alligators are found In North America and in China. The true 
Crocodiles of Africa and Asia have an American relative. The 
Snakes are widely distributed, the common grass snake {Tropi- 
donotus natrix) ranging from Sweden to Algeria. 




Fig. 182. The sidewinder or horned rattler {Crotalus cerastes). (Courtesy of Chas. 

Bogert.) 

Anatomy and Locomotion. — The Reptiles vary from the limbless 
Snake to the Lizards and Crocodiles which have well-developed 
limbs and a powerful tail. 

The oddest appearing forms are of course the Turtles. In the 
Chelonia both dorsal and ventral surfaces are covered by large 
horny plates. The scales are confined to the head, neck, limbs and 
tail. The Lizards and Snakes have horny plates covering their 
entire surface. In the skin of the geckos there are minute hard 
bodies intermediate between cartilage and bone. In the Crocodilia 
the whole surface is covered with horny plates underlaid with a pad 
of dermal connective tissue. In all Reptiles, except the Crocodilia, 
a periodical moult or ecdysis occurs. This casting of the old skin 
is done completely in Snakes and some Lizards, while in other 
Reptiles it is by degrees. 

Lizards move by means of their limbs and tail. Snakes have an 
undulatory movement on land and are able to swim very well. 
The aquatic Chelonia utilize their legs very effectively in swimming. 
Crocodilia depend upon limbs and tail and are able to swim with 
rapidity. On land their activity is much reduced but they are 
surprisingly quick in seizing prey and in the use of their powerful 
tail. 

Digestive System. — For the most part Lizards are non-poison- 
ous. The Mexican beaded Lizards have grooved teeth and are 
supplied with poison glands. Snakes rarely have premaxillary 
teeth. The vipers have a single large curved hollow poison fang 



326 REPTILIA 

with small reserve fangs at its base. This is moved to a vertical 
position when a snake opens its mouth to strike its prey. In the 
Chelonia there are no teeth but the horny jaws resemble a bird's 
beak. The Crocodilia have many conical hollow teeth on the pre- 
maxillae, maxillae and dentary. 

The tongues of certain Lizards are forked and retractile as in 
Snakes. The chameleon has an extremely long club-shaped tongue. 
In Snakes the tongue is extremely slender and is utilized as a tactile 
organ. Some hold that it is sensitive to sound vibrations. 

In the esophagus of turtles there are large horny recurved papil- 
lae. Crocodilia and Chelonia have a gizzard-like stomach. In 
Lizards and Snakes a rudimentary cecum is found at the anterior 
end of the large intestine. 

Respiratory System. — In the Snakes and some snake-like Lizards 
there is a great reduction in the size of the left lung. Chameleons 
have inflatable air-sacs which enable them to puff up and startle 
their enemies. The Crocodilia and Chelonia have large and well- 
developed lungs. 

In the Crocodilia the nostrils are at the upper end of the snout 
and can be closed by two valves. In front of the choanae, two soft 
" palatal folds " shut off the mouth from the pharynx. When a 
crocodilian is drowning its prey, it can push the glottis anteriorly to 
meet the posterior nares, and then respire comfortably. 

Old ma.\e gavials have a cartilaginous hump containing air which, 
situated at the tip of the snout, enables them to remain under water 
longer than younger animals. 

Superficial Differences between the Crocodilia 

Alligator. Crocodile. 

Exposes four points above water Exposes snout and neck crest when 

when floating — the eyes and the floating, 
nostrils. 

Fourth tooth from front bites into Fourth lower tooth from front pro- 
socket in upper jaw; in older ani- jects slightly outward and fits in- 
mals it may pierce jaw and show to grooved notch in outer edge of 
from above. upper jaw. 

Makes nest of sticks and grass. Makes nest in sand. 

Less active and vicious. More active and vicious. 

The caimans may have a blunt snout like the alligator or a 
pointed one like the crocodile. They also have the fourth tooth of 



REPTILIA 



327 



the lower jaw fitting into a socket. The gavial has a decidedly long 
and pointed snout and the first and fourth lower teeth bite into 
grooves in the upper jaw. 

Voice. — Snakes and lizards have no vocal cords, but hiss through 
the nose. Crocodilia roar and the tortoise of the Galapagos Islands 
bellows. 

Circulatory System. — xAll Reptilia have a four-chambered heart, 
but with the exception of the Crocodilia the ventricular septum is 
perforated. The red corpuscles of snake blood are 11 microns long, 
approximately the same as in frog blood, but those of the lizard are 
about 16 microns in length. 

Excretory System. — The kidneys are not always symmetrical in 
Reptiles, in the Snakes for example being elongated and band-like. 
The kidneys of Lizards are fused in the mid-line. A urinary bladder 
(usually bi-lobed) is found in Lizards and Chelonians, but is lacking 
in Snakes and Crocodiles. The urine is rich in salts and solidifies 
quickly on reaching the air as in the case of birds. 

Reproductive System. — Fertilization is internal in the Reptilia, 
which have either a bifid or a median solid penis. Many Lizards 
and the majority of Snakes are viviparous but the Crocodilia and 
Chelonia are oviparous. 

Care of the Young. — Crocodilia and Chelonia deposit their eggs 
in nests of sand or twigs and grass, and return to them periodically. 
The female python protects her eggs by coiling around them, her 
temperature rising several degrees during the process to promote 
hatching. 

Nervous System and Sense Organs. — In the Reptilia the brain 
has distinctly advanced from the amphibian type. The cerebral 
hemispheres have developed greatly but the cerebellum remains 
small. The eyes are large and the ears well developed, except in the 
Snakes where a middle-ear is absent. Tactile, olfactory and 
gustatory senses are well developed. The Turtle is surprisingly 
sensitive to taps on its shell. 

Rattle of the Rattlesnake. — Several species of snakes, including 
the bushmaster and the copperhead, have a large horny spine at 
the base of the tail. In the rattlesnake after the first year, three 
moults occur annually and at each moult a new rattle is formed. 
Considering the first ring to represent the first year, the age of a 
rattlesnake may be determined by allowing three rings for each 
year. The possibility of accidental loss of a segment or two must 
of course be considered. 



328 REPTILIA 

Poisonous Reptiles. — With the exception of the beaded Lizards, 
the Lacertilia are not poisonous. A Bornean Lizard, Lanthanotus, 
is suspected of being poisonous. Heloderma produces painful 
swellings in man, but its venom has no hemolytic action. 

The salivary glands of Snakes are differentiated into organs for 
the formation of powerful poisons. In the Australian black snake 
they act on the bloody causing intravascular clotting; some of this 
class also contain hemolytic substances. The arterial and venous 
walls are broken down and the blood oozes out. Gangrene may set 
in. Cytolysins act on red cells, white cells and the endothelium of 
the blood vessels. 

The other class, typified by the cobra, cause a paralysis of 
respiration. According to Cushney and Yagi, the action of cobra 
venom is like that of curare in that it paralyzes nerve endings. 
Noguchi states that in the case of cobra venom toxic action must 
be ascribed to neurotoxin. Poisoned animals suffer from motor 
paralysis. 

The chief local effect produced by rattlesnake and water moc- 
casin venom is, according to Noguchi, the escape of red blood 
corpuscles from the vessels. Hemorrhages are not restricted to 
the site of the injection of the venom. Animals killed with snake 
venom decompose rapidly because of the decrease in bactericidal 
power of the blood, caused by the venom. 

Toxicity. — According to Barbour the common laboratory stand- 
ard of toxicity ^ is the minimal lethal dose per pigeon. The poison 
of sea-snakes which is dangerous to man instantly kills fish. Turtles 
are almost as susceptible to all venoms as fish. Worms, Insects 
and Echinoderms are only slightly susceptible to snake venoms. 
While snakes and frogs quickly succumb to cobra venom, they are 
relatively insusceptible to the bites of rattlers and moccasins. 
The digestive juices destroy most snake venoms, but poisons of the 
cobra, the Old World Vipers, and the Australian black snake are 
resistant. 

^ Philpott (Proc. Soc. for Exp. Biol, and Med., vol. 26, pp. 522-523, 1929) has 
shown that the venom of the Texas rattlesnake {Crotalus atrox) in dilutions of 0.00025 
gm. per cc. had an immediate lethal effect on Paramecium caudatum, Stentor coeruleus 
and Bursaria truncatella. Action was slow in effect on Volvox spermatosphara and 
Oxytricha fallax, and was only temporary and slight in Chilomonas Paramecium. 
Coleps hirtus, Podophyrafixa and Dileptus gigas were unaffected. The minimum lethal 
dose of Agkistrodon piscivorus (moccasin) for Paramecium caudatum was 0.0000014 
gm., and for the venom of the fer-de-lance {Bothrops atrox) was 0.0000125 gm. 



REPTILIA 329 

Treatment of Snake Bite. — If administered very soon after the 
person is bitten, anti-venin serum is effective. A tight ligature, 
preferably of rubber, should be placed above the wound, but must 
not be left on more than half an hour at a time or gangrene will set 
in. The wound should be cut open with a knife or razor blade and 
may be sucked although this is unsafe if a person has sores in his 
mouth. A strong potassium permanganate solution is injected or 
poured upon the wound and serum is administered if available. 
After the first few moments potassium permanganate is not effective.' 
Subsequent treatment should include the draining of a wound for 
two weeks at least. 

Most engineers and explorers now carry into territory where 
rattlers and moccasins abound, antivenins, a little vial o{ potassium 
permanganate crystals^ a scalpel or razor-blade to cut open the wound, 
bandages, and a tourniquet. However, if one wears boots or puttees, 
he is usually quite well protected. Hypodermic injections of strych- 
nine are useful as a stimulant. It is held by some that small doses 
of alcohol are beneficial. This is a pernicious belief, as the adminis- 
tration of alcohol is likely to hasten death by distributing the venom 
more rapidly in the blood vessels. Caffeine (strong coffee) and 
strychnine are beneficial in relieving from giddiness and stupor. 

Susceptibility of Snakes to Poison. — The snake is not poisoned 
by amounts of digitalis fatal to the frog. Its tissues are not sus- 
ceptible, as isolated hearts behave the same. Cayenne pepper, 
fresh slaked lime and powdered sulphur are worthless as snake 
repellents. Snakes are immune to tear-gases and to poison gases 
including phosgene and chlorin. They are, however, susceptible 
very quickly to chloroform and also to mustard-gas. 

Do Mother Snakes Swallow their Young? — This question is one 
that has often been propounded. There is absolutely no doubt that 
snakes do swallow other snakes and that they may even, when 
alarmed, swallow their own young. Many people have testified to 
seeing the old snake swallow little ones, but no one has ever reported 
the interesting phenomenon of the little snakes returning to the 
light of day. Perhaps they do! 

1 Dr. A. M. Reese is studying the effects of potassium permanganate on mam- 
mals receiving injections of snake venom that would ordinarily be toxic. 



330 REPTILIA 

Some Superstitions That Exist Regarding Snakes. ^ — 

"l. Snakes do not suck or milk cows. This is next to a physical 
impossibility and science has no authentic record to prove it 
true. 

" 2. Hoop snakes do not exist. Substantial rewards have been offered 
for specimens and a demonstration of* rolling' but no one has 
tried to claim the reward. 

"3. Snakes do not charm birds but cause them to become so excited 
or nervous that they lose reason or instinct of protection. 
This is especially true of nesting birds. 

"4. When a snake is killed some vital organ or organs stop function- 
ing, but all cells are not killed. These living cells function 
by reflex action for a varying period of time dependent on the 
kind of cells, and not dependent on the action of the sunlight. 

" 5. Snakes do chase people, especially the blue racer. It is, however, 
a coward and will run equally fast in the opposite direction 
if the pursued become the pursuer. 

"6. Snakes do not sting or bite with any part of the body except the 
teeth. The tongue is sensory in function, being the seat of 
the senses of touch, taste and perhaps smell. 

"7. No snake or part thereof has any medicinal property which can- 
not be found in some other material. For instance sweet oil 
is just as good as rattler oil, and not as repulsive to most 
people. This belief has been imposed upon the people by 
'fakes' or 'quack doctors.' They are not even considered by 
reputable physicians. 

"8. Green is not a warning color against poisonous snakes. 

"9. Snakes are blind only during the process of molting or when the 
old skin is loose and is being shed because a new skin has 
developed underneath. 

" 10. A horse-hair rope will not act as a barrier to a rattlesnake. This 
has been demonstrated many times by actual test," 

Fossil Relatives. Super-Order I. Cotylosauria. — Geologically 
the oldest known reptiles, appearing in the Carboniferous and dis- 
appearing in the Triassic. Skulls completely roofed, v^^ith no 
lateral temporal vacuities. Pelvis, flattened. Resembled Stego- 
cephalia in presence of pectoral cleithrum. Heavy neural arches. 
Example: Seymouria. 

' By permission of R. D. Casselberry from the Pennsylvania State College, Cor- 
respondence Study Department, Zoology 35 C, Lesson 7. 



REPTILIA 331 

Super-Order 11. Chelonia. (Gr. chelone^ a tortoise.) — Fossil 
relatives of the turtles include a Permian species Eubotosaurus, 
found in S. Africa, which had teeth and widened ribs. 

Super-Order III. Therapsida. {Anomodontia, Theromorpha.) 
(Gr. ther, a wild beast; morphe^ form.) — Single lateral temporal 
vacuity below post-orbital and squamosal. Brain case high, ear 
low, columella articulates with quadrate. Lower jaw flattened, 
with loosely articulated bones. Fossils found in Permian and to 
the Triassic age, chiefly from Africa and North America. 

The Mammalia are supposed to have arisen from this order, 
possibly by way of the Theriodontia, which were carnivorous, with 
teeth resembling the incisors, canines and molars of mammals. 
The Monotremata (see p. 373) have been compared with the Therio- 
dontia, in support of such a theory. Examples: {Dicynodon^ 
Cynognathus^ Galepus, Ophiacodon). 

Super-Order IV. Sauropterygia. (Gr, sauros^ a XvL?ixdi\pterygia^ 
fins.) — /\quatic reptiles with a single temporal vacuity, bounded by 
the post-orbital squamosal arch. Single coracoids, meeting in a 
ventral symphysis. The cervical region is extremely long, and the 
caudal portion of the spinal column is very short. Sauropterygia 
range from the Triassic to the Cretaceous. 

Super-Order V. Ichthyopterygia. {Gr. ichthysy & fish; ptejjgia, 
fins.) (Ichthyosauria.) — Marine reptiles with a single lateral 
temporal vacuity, a large head, elongated jaws, teeth in grooves, no 
neck, and a long tail resembling a fish. They had two pairs of 
paddle-like limbs, no sacrum, primitive pelvis, no sternum, but well- 
developed abdominal ribs. They are of the Mesozoic age, ranging 
from the Triassic to the Upper Cretaceous. 

Super-Order VI. Archosauria. — Several Orders belong to this 
super-order, which includes the reptiles that have two lateral tem- 
poral vacuities in the skull. 

Order i. — Thecodontia are the earliest Reptiles to show a diapsid 
skull with two lateral temporal vacuities. 

07-der 2. — Rhyncocephalia appeared in the Permian, with maxi- 
mum development in the Triassic. 

Order J. Dinosauria. (Gr. deinos, terrible; sauros, a lizard.) — 
These Mesozoic land reptiles were among the largest, reaching a 
length of one hundred feet and a height of twenty feet. The earliest 
species, in the Triassic, were carnivorous. Another branch, the 
Sauropoda, include gigantic herbivores. A herbivorous branch, the 



33^ 



REPTILIA 



Ornithopoda, had a bird-like beak, and the Orthopoda had pneumatic 
bones and a bird-like pubis. 

Order 4. Crocodilia. — Fossil Crocodilia are found in the Triassic 
strata. Huxley traced an " almost unbroken series " of Crocodilia 
from the Triassic down. 

Order 5. Pterodactyla or Pterosauria. (Gr. pteron, a wing; and 
sauros, a lizard.) — The Pterosauria were adapted for flight, having 
a long neck and a pair of bat-like leathery wings. The bones were 
light and hollow, the breast bone was keeled. The earlier forms had 
sharp teeth. They varied in size from that of a sparrow to the 
Pterodactyl with a twenty-four foot wing stretch. The largest 
forms lacked teeth and had a short tail. 

Order 6. Squamata. — The Squamata are geologically the most 
recent of the Reptilia now persistent. 

Sub-Order {a). Lacertilia. — There are a few fossil lizards in the 
Jurassic, but the majority began with the Tertiary. 

Sub-Order {b). Ophidia. — Fossil snakes appeared in the Ter- 
tiary strata. 

Sub-Order (c). Pythonomorpha. — These extinct forms had a 
snake-like body with paddle-like limbs used in swimming. They 
reached a length of over fifty feet {Mososaurus). The skull re- 
sembled that of the Lacertilia. 

Adaptations of Reptilia. — The Crocodilia have protective bony 
plates in the skin, sharp teeth, strong jaws and a muscular tail. A 
valve in the throat shutting off the mouth from the pharynx (see p. 
326) enables them to submerge their prey and still breathe with 
ease. The Chelonia have a strong compact box-like shell and 
powerful cutting jaws. Large lungs enable them to remain under 
water for some time. Lacertilia have rapid locomotion. In some 
protective coloration is evident. The long tail is a storehouse for 
food and in many species is broken off and left when enemies are 
pressing. Ophidia have displaceable jaw bones and loose ribs, 
permitting the animal to swallow prey larger than itself. The 
glottis is anterior to the mouth, enabling the snakes to breathe while 
swallowing. The teeth are recurved so that the prey cannot escape. 
Snakes kill by crushing or utilizing poison glands. 

Economic Importance of Reptilia. — Crocodilia furnish skins that 
are used in the manufacture of shoes, bags, pocket books and belts. 
They feed on fish and in the case of the Asiatic and African crocodiles, 
destroy many human lives. The flesh of crocodiles is said to be 



REPTILIA 23:^ 

unpalatable on account of its strong musky flavor. (Clark.) Alli- 
gators are occasionally eaten by the Southern negroes. Lacertilia 
are important in the extermination of injurious insects and some 
species (iguana) are utilized as food. Ophidia are in general bene- 
ficial in exterminating harmful rodents and insects. The poisonous 
snakes are relatively few, but cause twenty-five thousand or more 
deaths annually, most of them in India. 

References on Reptilia 

Barbour, T. 1926. Reptiles and Amphibians. Houghton Mifflin Co. 
DiTMARS, R. L. 1907. The Reptile Book. New York. 
DiTMARS, R. L. 1 9 10. Reptiles of the World. New York. 
Reese, A. M. 191 5. The Alligator and its Allies. New York. 
Surface, H. A. First Report on the Economic Features of the Turtles 

of Penna. Zool. Bull, of the Dept. of Agr. of Penna., Harrisburg, 

Aug. -Sept. 
Surface, H. A. 1907. The Lizards of Pennsylvania. Bull, of the 

Dept. of Agr. of Penna., Harrisburg. 



CHAPTER XVIII 



AVES 



Birds are more highly specialized in structure and habits than 
even the mammals. They, like the insects, are perfectly adapted to 
flight. Geological records and some vestigial structures (scales) 
indicate the close relationship of birds to reptiles. 

So widely distributed are birds and so familiar to our sight and 
hearing, that it is difficult to conceive of a civilization without them, 
or what would happen to that civilization, did they not exist. Eco- 
nomically, birds are of the greatest significance, since they not only 
serve as food, but are the most important agencies in keeping 
insects from utterly destroying the food of men. More than 23,000 
species of birds have been described. They have been classified 
according to types of bills and claws and in some cases from their 
colors and habits. The classification is variable and unreliable. 

Subclass I. Archeomithes. — Fossil birds. 

The fossil, reptile-like birds belonging to the genus Archeopteryx 
are quite evidently connecting types between the reptiles and the 
birds. (See Fossil Relatives of Birds, page 370.) 

Subclass II. Neomithes. — Recent birds. 

Among the more recent birds, there are two Orders that exist as 
fossils, and will be described later, under the heading of Hesper- 
ornithiformes, and Ichthyornithiformes. (See page 371.) 

The remainder of the Subclass Neornithes will be arbitrarily 
divided into two divisions, the running birds, called Ratitae, and 
the flying birds, or Carinatae. 

Natural History 

Division A. The Ratitae 

The Ratitae are the running birds with reduced wings. Exam- 
ples: ostrich, emu, cassowary, rhea. 

Characteristics. — i. Raft-like or keelless breast bone. 

2. Wings rudimentary or not large enough for flight. 

3. Foot two-toed, large leg fitted for running. 

334 



AVES 33 s 

The ostrich reaches a height of 6 to 8 feet and may weigh 450 
pounds. Its single stride when running is 25 feet and it runs 60 
miles per hour, but in circles, and is easily caught. It uses its two- 
toed feet in defense and can kick a horse to the ground. Ostriches 
do not hide their heads in the sand, but they do thrust them into 
the sand in search of water which they frequently find. The eggs 
are said to contain as much food as 24 hens' eggs. African savages 
utilize the egg shells as containers. Ostrich plumes are extremely 
valuable or less so according to the fashion dictated by milady. 
High tariff, overproduction, and post-war depression, caused the 
price of feathers to drop from I14 to less than $4 a pound. There 
are now about 250,000 birds on African ostrich farms. In the 
United States, ostriches have been bred since 1882. The plumes are 
plucked or clipped twice a year. (Figure 183.) 

The emu is an Australian form next to the ostrich in size. It 
lacks the ornamental wings and tail plumage of the ostrich. The 
cassowaries inhabit Australia and the Malay Archipelago. They 
have long silky plumage and live in thickly wooded regions. Some- 
times they take to the water for bathing. The female cassowary is 
larger than the male. Both sexes are black. The plumage is made 
into rugs, mats and head ornaments. The r-heas, the New World 
ostriches, live on the pampas of the Argentine Republic, Southern 
Brazil, Bolivia and Paraguay. Their wings are better developed 
than those of the ostrich. They flap them as they run. 

The elephant birds, now extinct, were existent in Madagascar 
400 years ago. They were flightless and about 7 feet tall. Their 
eggs, found in Madagascar, are 13x9 inches with a capacity of two 
gallons. A single Aepyornis egg was equal to 12 ostrich eggs, 288 
hens' eggs, or 500,000 humming-bird eggs. The natives of Mada- 
gascar claim that elephant birds are still left in the interior, but this 
is doubted. The 7noa {Dinorthiformes), now extinct, lived in New 
Zealand 500 years ago. It was like the ostrich, but with heavier 
bones and rudimentary wings. The kiwis of New Zealand belong 
to the genus Apteryx, and are not completely wingless. They are 
probably related to the cassowaries. Their voice is a shrill sound — 
KI-WI. The nostrils are at the tip of the bill. The male incubates 
the eggs which are about one-fifth the body weight of the bird. 

Tinamousy which are found from South America to Mexico, are 
classed by some authorities near the ostriches and considered 
Ratitae; while others class them as an aberrant family of the order 



33^ 



AVES 




J^ 




Fig. 183. Group of Ratite birds. J, Rhea, R/iea americana; B, the Kiwi, 
yipteryx australis; C, Cassowary, Casuarius uniappendicidatus; D, Ostrich, Struthio 
camelus; E, Emeu, Droaemus novae-hollandae. (Newman, Vertebrate Zoology. Re- 
drawn after Evans. Courtesy of The Macmillan Co.) 



AVES 337 

Galliformes, among the Carinatae. The wings are short and 
rounded; the keel of the sternum is well developed and the pectoral 
muscles large. The tail feathers are reduced. Strong, swift run- 
ners, they can rise, after considerable effort, to 150 feet and fly or 
plane a thousand yards. Probably the tinamous represents an 
intermediate condition between the flying birds and the running 
or flightless birds. 

DivisioN^ B. The Carinatae 

The Carinatae include most of our common flying birds. 
Characteristics. — They have a keeled sternum and are for the 
most part fliers. 

Classification (Modified from the A. O. U. Check List).— 

Order i. Pygopodes — auks, grebes and loons, penguins. 

Order 2. Longipennes— gulls and terns. 

Order 3. Tubinares — petrels and albatross. 

Order 4. Steganopodes — frigates, cormorants and pelicans. 

Order 5. Anseres — wild geese and swans. 

Order 6. Odontoglossae — flamingo. 

Order 7. Herodiones — storks, herons, ibises, and spoon-bills. 

Order 8. Paludicolae — cranes, rails and coots. 

Order 9. Limicolae — plovers and snipes. 

Order 10. Gallinae — pheasants, pea-fowls, chickens, turkeys. 

Order 11. Columbae — pigeons and doves. 

Order 12. Raptores — hawks and owls. 

Order 13. Psittaci — parrots and parokeets. 

Order 14. Coccyges — kingfishers and cuckoos. 

Order 15. Pici — woodpeckers. 

Order 16. Machrochires — humming birds, swifts, nighthawks, and 

whip-poor-wills. 
Order 17. Passeres — flycatchers, larks, jays, orioles, and grackles. 

Order 1. Pygopodes. — Looyis are large, often 24-28 inches long, 
and the most expert diving birds. Their cry is weird, laughing, loud 
and melancholy, resembling the dying wail of a person. The small 
European grebe is called the " dabchick " because it tucks its young 
under its wings when it dives to escape enemies. Grebes resemble 
penguins more than loons. 

The " Great Auk" once abundant on the islands north of Scot- 
land and near Newfoundland, has been killed off, feathers being the 



338 



AVES 



chief attraction. The eggs have been collected, resulting in no 
evidence of their presence, other than bones. The last living speci- 
men was seen in 1844. 

The penguins (Figure 184), marine birds found in the Antarctic 
seas, have paddlelike wings which work from the shoulder in a rotary 
fashion. The legs are set far back, and the feet are used for 
steering, not propulsion. Penguins have almost waterproof feathers. 
Their plentiful subcutaneous fat produces a marketable oil. The 
male aids in incubating the eggs which require 6 weeks to hatch, 
and the young are blind. 




Fig. 184. Galapagos penguin. (Courtesy of N. Y. Zool. Soc.) 



Order 2. Longipennes. — Gul/s (Figure 185, A and B) are 
aquatic, mainly oceanic, of medium size, with long pointed wings 
and webbed feet. They are scavengers of the ocean, feeding from 
the surface. Terns are more active than gulls. Their bodies are 
slender and they have long-forked tails and pointed bills. They 
nest on islands in colonies. 

Order 3. Tubinares. — The petrels , " Mother Carey's Chick- 
ens," are widely ranging sea birds of moderate size with long narrow 
wings and a hooked bill. The " stormy petrel," the smallest of 



AVES 



339 



web-footed birds, Is deemed a prophet of rough weather. The 
albatross^ immortalized by Coleridge in his " Rime of the Ancient 
Mariner," is one of the largest of the flying birds with a wing stretch 
of from twelve to fifteen feet and may weigh twenty pounds. It 
is able to fly and soar for hours. The gannets are sea birds fre- 
quenting the colder regions, coming ashore during stormy weather. 




— JUk^. 



Black Tern 



=■ fa-* 



Herring Gull 



Fig. 185. A, black tern. 5, herring gull. (From L. A. Fuertes. Courtesy of 

Slingerland-Comstock Publishing Co.) 

Order 4. Steganopodes. — The cormorants are large sea-coast 
birds. They are voracious fish eaters, coming to inland lakes during 
the breeding season. The Chinese tame them and use them in 
catching fish. The darters or " snake birds " are not marine, but 
frequent inlets of the sea and fresh water lakes. They excel as 
divers, but are poor flyers. The frigate birds or " man-of-war 
birds " are true sea birds, only coming to shore to nest. They have 
long wings, and an extremely long tail. Their legs are weak, but 
they are remarkable flyers. The pelicans are large tropical birds. 
The large bill and lower jaw are provided with large pouches in 
which are stored fish. They are known to many by their stubby tail 
and short legs. (Figure i86.) 

Order 5. Anseriformes. — The swans are large birds, graceful in 
form and movement. They are pugnacious and quarrelsome. 
Their voice is " like a blast from a French horn," but musical when 
given by a large flock in chorus. The trumpeter-swan is white. 
The geese are intermediate between swans and ducks in some 
characteristics, especially in the length of the neck. (Figure 187.) 
Some ducks are feathered brilliantly. One of the most handsome 



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is the male mandarin duck. Diving birds can remain under water 
about one minute. Eider ducks are natives of the north and are the 
best known and most valuable of the duck family. Many eider 
ducks are slaughtered to secure the much prized breast feathers, 




Fig. 1 86. Pelican. (Courtesy of E. R. Sanborn and N. Y. Zool. Soc.) 



" eider-down." The mergansers^ or fish ducks, differ from true 
ducks in having more slender bodies, grebe-like necks, and long 
compressed bills with serrated edges. They are fish eaters and 
hence not as edible as other ducks, but are much sought by hunters 
on account of their " quick-get-away." (Figure 187, A^ B, C, D.) 

Order 6. Odontoglossae. — Flamingoes are large, long-legged, 
long-necked birds with pink plumage. They are good flyers, but 
are better known as waders. They scoop up fish and shell-fish, 
straining them out as the water and mud pass through holes in the 
lower part of their beak. 

Order 7. Herodiones. — Herons, ibises, and storks bear a strong 
resemblance to one another. The ibis fed on snails in the Nile, 
and was worshipped. (See Schistosoma, page 77.) The long legs, 
collapsible necks, and flapping wings of storks are well known to 
all children. The stork migrates long distances. (See p. 366.) 



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The spoonbill is stork-like with a spoon-shaped bill that easily 
captures insect prey, larvae, fish, frogs, etc. It is found in the trop- 
ics. The tropic birds are found in the tropic oceans, flying hundreds 
of miles from land and taking refuge on ships or floating debris. 
(Figure 188.) 




Fig. 187. A, black duck. 5, Canada goose. C, greater scaup. D, mallard ducks. 
(From L. A. Fuertes. Courtesy of Slingerland-Comstock Publishing Co.) 



Orders. Paludicolae. — The sandhill crane is the most abun- 
dant and largest of this species found in America. The great 
bustard is the largest of European birds, being about 45 inches long 
and weighing about 30 pounds. It looks like a goose, but has a 
head and bill resembling the crane. The sun bitterns are small, like 
the rails, with short legs, thin neck, a large head and a long, pointed 
bill. The head is sunk on the body, when at rest, giving the bird a 
neckless appearance. The rails resemble the quail and the plover. 
(Figure 188, A, B, C, D.) 

Order 9. Limicolae. — The Limicolae are marsh and shore birds, 
with long necks, long slender bills, rather long slender legs, short tails 



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and wings. They are usually brown or gray, with blotches of white. 
The hind toe is, with one exception, lacking or extremely short. 
There are about 75 species of these mud-dwellers in the United 
States. 




Fig. 188. y/, great blue heron. 5, night heron. C, killdeer. D, ring-necked plover 
(From L. A. Fuertes. Courtesy of Slingerland-Comstock Publishing Co.) 



The phalaropes are small in size with lobed toes. The female is 
more brilliantly colored than the male (which is uncommon in birds) 
and does the courting. The male incubates the eggs. The -plover, 
or killdeer, is one of the most beautiful of the shore birds, being 
found along inland pools and ponds. The American golden plover 
is found along the seashore and frequenting the banks of tide pools. 
It migrates tremendous distances. (See p. Z^(y^ 



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Other members of this order are the American woodcock^ with its 
long sensitive, probe-like beak, used in procuring earthworms; the 
Wilson's snipe, the sandpipers, and the curlews. 

Order 10. Gallinae. — This order includes two families of un- 
familiar birds, the brush turkeys {Megapodes) of Australia and New 
Guinea and the curassows and guans ( Cracidoe) of tropical America. 




Fig. 189. //, snipe. 5, spotted sandpiper. C, bob white. D, spruce grouse. (From 
L. A. Fuertes. Courtesv of Slingerland-Comstock Publishing Co.) 

The Gallinaceous birds include the common fowl and game birds 
such as wild turkeys, grouse, partridges, bob-whites, and ptarmigans. 
The most highly specialized types are characterized by brilliant 
plumage, being the males of the golden and Lady Amherst pheasants, 
native to South China and Eastern Thibet. 

The common bob-white or quail \s> an extremely important weed- 
seed and insect destroying bird. The rufed grouse are strong flyers 
and their flesh is extremely palatable. Ruffed grouse are susceptible 
to the disease tularemia. Wild turkeys are still found in the East, 



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in Pennsylvania and West Virginia. Ptarmigans turn snow white 
in winter. Pea fowls are oriental birds, domesticated all over the 
world. 

There are four distinct species of the jungle fowls ^ all native to 
the jungles of the Indo-Malayan regions. The domestic fowl has 
come from the red jungle fowl of this species. The black breasted 
game fowl ho.?, retained more than the others the original characteris- 
tics of its ancestors. The most different from the primitive is the 
Japanese tosa fowl, in which the tail feathers have been known to 
reach a length of fifteen feet, and also the Cochins, with their short, 
plump appearance and feathered shanks. (See p. 494, Domesti- 
cated Animals.) The Greeks were addicted to the sport of cock- 
and quail-fights. The Chinese and Malays still have quail-fights. 
(Consult D'A. W. Thompson, " A Glossary of Greek Birds." 
Oxford, 1895.) 

Order 11. Columbae. (Pigeons, doves.) — The dodos, recently 
extinct, were large, peculiar looking pigeons. Pictures of them, and 
their bones, prove them to be odd looking, short, plump with an 
eagle-like beak and very little plumage. The true pigeons are a 
. large family widely distributed * The best known are the carrier 

/\ pigeons, rock pigeons and the great crowned pigeon. The rock 
pigeon or rock dove is the species from which most fancy breeds of 
domestic pigeons have come. When they are allowed to interbreed 
freely the offspring revert to the characters of their wild ancestors. 

Homing pigeons were used by the Greeks who probably learned 
the art of training pigeons from the Persians. The Sultan estab- 
lished a message system using pigeons, which lasted in Bagdad from 
1 150 to 1258. Homing pigeons were used in transmitting mes- 
sages by the Roman general Decimus Julius Brutus who was then 
besieged by Mark i\.ntony. During the World War the combatants 
used over five hundred thousand homing pigeons, the American 
Army utilizing twenty thousand. Our homers are equipped by the 
Signal Corps with " pigeon whistles " to frighten away hawks. 

The passenger pigeons (Figure 190) once lived in flocks of 
enormous numbers. Wilson, an early American ornithologist, 
estimated one flock to include two billion individuals.'* The last 
passenger pigeon, hatched in the Cincinnati Zoo, died there on 

*A town in Michigan marketed (1869-1870) in two years 15,840,000 pigeons. 
Hornaday. (Our Vanishing Wild Life.) 



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September i, 1914, at the age of twenty-six years. The passenger 
pigeon had a pointed tail and nested several feet from the ground. 
The mourning dove is a beautiful bird, and although it has a 
square tail is sometimes confused with the passenger pigeon. It is 
an important enemy of weed seeds. It nests on or near the ground. 




Fig. 190. Passenger pigeons. (Courtesy of Field Museum of Natural History.) 



Order 12. Raptores. — Eagles, hawks, falcons, owls and condors 
are characterized by hooked sharp beaks, strong talons, large crop 
and markedly predaceous habits. 

The golden eagle has dark brown plumage. It is nearly one 
yard long, with a wing spread of nearly seven feet. It destroys 
poultry, young deer, and small mammals. It is still found in the 
Rockies. The American^ or " bald " eagle^ our national bird, has a 
white head and tail in its fourth season. It lives along rivers and 
feeds on fish, although it is not above the occasional capture of a 
lamb. (Figure 191.) 

The sharp-shinned hawk and Cooper s hawk (Figure 192) are 
the common hawks most responsible for the loss of game and poultry, 
while the duck hawk is extremely destructive to water fowl. 
Sparrow hawks and pigeon hawks are important enemies of the 
English sparrow, and beneficial rodent exterminators, but attack 
some valuable birds. 



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The American goshawk^ a native of Canada, coming to the 
United States only in the winter, is a bold destroyer of game birds, 
especially the ptarmigan. It has been known to escape with a 
freshly killed chicken or even to follow the owner into the house and 




Fig. 191. Eagle family. The female is ripping up a fish to feed to her three 
eaglets, whose white heads are ranged before her. The inbending of the left foot of 
the male, seen taking off in the air, was due to an old wound. He was wantonly killed 
in the following November. Vermilion, April 27, 1924, at about six in the evening. 
By F. H. Herrick. American Eagle Series of Western Reserve University. 



snatch it from the table (Fisher). It reaches a length of twenty-five 
inches. The ancient sport of falconry is being revived somewhat 
abroad and in the United States, and goshawks are the favorite 
" falcons." In Turkestan, sparrow-hawks, goshawks, buzzards, 



AVES 347 

kites and eagles have been used in falconry tor centuries. Golden 
eagles are used to hunt foxes for their pelts. 




Fig. 192. Young Cooper's hawk. (Courtesy of W. E. Rumsey and A. J. Dadisman.) 



References on Falconry 

Blanc, M. E. 1895. Hunting with birds of prey. Pop. So. Men., vol. 

47, no. 6, pp. 818-823, Oct. 
FuERTES, L. A. 1920. Falconry, the sport of kings. Nat. Geog., Dec. 
Goodman, G. G. 1929. Falconing. Nat. Hist., July-Aug. 
Lattimore, O. 1929. The desert road to Turkestan. Nat. Geog., 

June. 

The Turkey buzzard (see Figure 193 C), seen in most of the 
Southern States, is valued by man on account of its importance as a 
scavenger. Laws once existed in some Southern States protecting 
the buzzard. It is suspected of carrying the germs of hog cholera. 

The Andean condor^ the Caltforntan condor and the king vulture^ 
all members of the group Falconiformes, are notable in their ability 



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to soar for hours. This capability has baffled physicists interested 
in the problems of aviation. 

The secretary birds are the strangest of the birds of prey. They 




Fig. 193. A, red-tailed hawk, 5, osprey or fish hawk. C, turkey buzzard. 
D, great gray owl. (From L. A. Fuertes. Courtesy of Slingerland-Comstock Publish- 
ing Co.) 

are long-legged, standing about four feet high and with great speed- 
ing ability. They are fond of snakes, but will eat lizards, frogs, 



AVES 349 

and insects. Distending a stiff wing, they receive the bite of a 
snake, stun the reptile and kill it. 

There are eighteen species of owls in the United States. Among 
the commonest forms are the barn owl, the long-eared owl, the barred 
owl, the great gray owl — an Arctic bird never found south of the Ohio 
River, and the screech owl. The great horned owl, sometimes called 
the " tiger of the air," is a bloodthirsty game killer. Besides killing 
poultry, it is of great importance as a destroyer of rodents. It is 
the only owl that can be considered an enemy of man. The snowy 
owl comes from the Arctic zone to the Northern part of the United 
States in the winter. It feeds upon wild game and rodents, but 
avoids poultry yards. The bun-owing owl is found in prairie dog 
holes in the Southwestern states. It does not prey upon the " dogs " 
but avoids them and their companions (?) the rattlesnakes. Bur- 
rowing owls are able to dig their own holes, and certainly do not 
go down into homes already occupied. 

Order 13. Psittaci. {Paj-rots and paroquets.) — The parrots are 
brilliantly colored with great ability to mimic. They live to a great 
age (seventy-five years) and learn to talk quite readily. At times 
they display remarkable memory for certain expletives uttered by 
their owners in moments of stress. The African Gray parrot with 
a red tail is the best talker. The brush-tongued parrots, found in 
Australasia, have an odd " brush " at the end of the tongue, adapted 
to feeding on honey. The paroquets are extremely small parrots 
found in the United States, in Florida. They feed on fruit and seeds. 
The macaws are large scarlet and blue birds with long pointed tails 
and horrible voices. The hyacinthine macaw of Brazil feeds on 
nuts of the palm, macuja, crushing them by means of its powerful 
beak. The cockatoos are usually snow-white, with long triangular 
erectile crests. They are frequently trained for vaudeville exhibi- 
tion. A giant black species from New Guinea with a slender 
cylindrical tongue, and an enormous beak, is able to open the 
excessively hard " canary nut." 

Order 14. Coccyges. — The cuckoos are best known from their 
peculiar habit of placing eggs in other birds' nests. Instead of 
building a nest of her own, the female lays the egg on the ground, 
then carries it in her bill to some other nest. This parasitic habit 
belongs to the Old World Cuckoo, for the American cuckoo builds 
its own nest. 

The Coraciae are sub-orders having affinities with the cuckoos 



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and the sparrows. They include the kingfishers and the horn-bills. 

The horn-bills are large birds using their enormous bills in wall- 
ing up nests. The male seals up the female in a hollow tree, feeding 
her through a small aperture. The kingfisher family includes three 
species in the United States. It nests in a hole dug horizontally 
into a bank of earth. Its food consists almost entirely of small 
fishes. The belted kingfisher is an enemy of trout and other fry 
at fish hatcheries. 

Order 15. Pici. — The woodpeckers and sapsuckers are the most 
familiar of our native birds. There are about twenty-five species 
of American woodpeckers. The flicker, or golden-winged wood- 
pecker, is a large bird which perches crosswise on limbs like the 
true perchers. It is also called the " yellow hammer " or "high- 
hole." Its stomach contents show over fifty per cent insect food, 
about forty per cent vegetable food, chiefly berries and seeds. The 
red-headed woodpecker, immortalized in Longfellow's " Hiawatha," 
is a showy creature with a brilliant crimson head and neck, white 
breast and black back and tail. Its food consists of ants, beetles, 
weed-seeds and fruits. It is particularly fond of beech-nuts. The 
downy woodpecker and the hairy woodpecker consume about seventy- 
five per cent insect food and about twenty-five per cent vegetable 
food, mostly weed-seeds and wild fruits. The yellow-bellied sap- 
sucker injures trees by girdling them. It drinks the sap exuding 
from its neatly formed squarish holes. In New England some 
orchard owners protect their trees with fine wire netting. This 
form is the most migratory of our woodpeckers. Toucans have 
enormous bills which, however, are extremely thin and light in 
weight. 

Order 16. Machrochires. — The Machrochires Include the whip- 
poor-will, night hawk and chimney swift which are exceedingly 
valuable as enemies of both day and night flying insects. (Figures 
194 and 195.) 

The humming-birds feed on insects and spiders and on the sap 
of trees in holes prepared by the sapsucker, as well as upon the 
nectar of flowers. Humming birds, although small, are exceedingly 
brave and pugnacious, and one pair of them will attack and drive 
to flight hawks and large snakes. The swifts are less attractive 
than humming birds and are often mistaken for swallows. They 
have a broad bill and wide mouth like the goat-suckers. 



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Fig. 194. Rufous hummingbird on nest. (Photo by W. L. and Irene Finley. Cour- 
tesy of National Park Service.) 




Fig. 195. Nest and eggs of ruby-throated humming bird. (Courtesy of Fred E. 

Brooks.) 



Order 17. Passeres. — This is the largest order of birds, con- 
taining over half the species. As the name indicates the forms are 
perching birds. The birds of paradise are the most brilliantly 
colored of the order. The great bird of paradise is the most beauti- 
ful of the species. The lyre-birds rival the birds of paradise in 
plumage construction, but are not so brilliant. 



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The blue-birds, robins and the thrushes {Fam. Turdidae) are 
important enemies of insects and worms. Robins are a bit injurious 
to cherries, since the dietary change offered by these (acid) fruits is 
so welcome to them. The chickadee {Fam. Paridae) is an extremely 
important enemy of insects, including aphids (plant-lice) and canker 
worms. 




Fig. 196. J, kingbird. B, wood thrush. C, chimney swift. D, horned lark. 
(Courtesy of Slingerland-Comstock Publishing Co.) 



The crows and jays {Fam. Corvidae) number over two hundred 
species. They eat fruits, insects, seeds and the eggs and young of 
other birds. 

The king-bird., the phoebe and the fly-catchers, crested and least 
{Fam. Ty7~annidae),2iX^ all extremely important insect destroyers. 



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The king-bird, however, is said to be an important enemy of honey- 
bees. 

Black-birds and orioles {Fam. Icteridae) are among the most 
beautiful of birds. The boboUyik of the south is an enemy of rice 
fields. In the north it is considered one of our sweetest singers. 
The orioles are extremely beautiful birds with peculiar nests hanging 
down considerable distances from boughs. The cow-bird has the 
habit of laying its eggs in the nests of other birds, particularly 
sparrows and warblers. 




Fig. 197. Young brown thrashers. (Courtesy of G. H. Roush.) 

The sparrows znd finches {Fam. Fringillidae) are all important 
destroyers of weed-seeds. The English sparrow, however, which 
was introduced into America in 185 1 has proved a menace to the eggs 
and young of our beneficial tree swallows. 

The shrikes or butcher birds {Fam. Laniidae) are important 
enemies of English sparrows and rodents, but on account of their 
habit of killing the small forms like the chickadee and the wren, 
must be considered injurious. They impale the bodies of their 
victims on twigs. 



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The swallows {Fam. Hirundinidae) are extremely efficient insect 
destroyers. Their relatives, the purple martins^ will readily take 
up their abode in bird houses. The mocking-birds, thrashers and 
wrens are beautiful singers and important enemies of insects. The 
warblers {Fajn. Mniotilitidae) include over one hundred species, 
about seventy-five of which are found in the United States. They 
are important enemies of insects. 




Fig. 198. Whitebreasted nuthatch. (Courtesy of F. E. Brooks.) 



The Anatomy and Physiology of Birds 

No animal has feathers except the bird. " A bird is known by 
its feathers." Every part of the organization is modified for aerial 
life. 

Characteristics. — i. Feathers. 

1. Sternum and shoulder girdle enlarged to support wing mus- 
cles. 

3. Forelimbs modified as wings. 



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4. Pelvic girdle and hind limbs adapted to support the body on 
the ground. 

5. Respiratory system developed to produce a higher tempera- 
ture than in any other animal. 

6. Absence of teeth. 

7. Loss of the left aortic arch. 

8. Right ovary and oviduct lost. 

9. Poorly developed olfactory organs. 

10. Extraordinary development of the eyes. 

Temperature ^ is lower in most lowly organized birds. There is 
a progressive gradation to the higher birds. The apteryx or kiwi, a 
wingless bird of New Zealand, has a temperature of 37.9° C. (100.2° 
F.). The emu, cassowary and penguin have a temperature of 
39.° C, the sparrows and warblers from 42° C. to 44° C. (107.6° 
F.), the common fowl, 40.6° C. The average of sparrows is 109.9° 
F., which is 10° above the temperature of man. (Figure 199.) 

Feathers have a hollow, transparent barrel, or quill, continuous 
with the shaft or rachis. The shaft is opaque, quadrangular in 
cross section and filled with a pithy substance. From the shaft 
above the quill arise lateral branches, known as barbs or rami. 
Barbs give off barbules and these in turn give off the barbicels 
which are hooked processes. The hooked processes produce the 
web and furnish it strength to resist or act upon the air. From the 
underside of some feathers at the juncture of the quill with the web- 
bearing portion is a secondary feather, the after shaft. There are 
three kinds of feathers: (i) Contour feathers (complete). (2) 
Down feathers, soft shaft, no barbs, serve to retain heat. Some 
have no shaft. (3) Filoplumes, degenerate, hairlike with few or no 
barbs. 

Feathers are derived from cornification of the inner layer of the 
epidermis. The papillae consist of external epidermis and internal 
dermis, the latter furnishing nutriment to the growing feathers. 
Epidermal scales of the birds arise similarly from papillae. 

Birds shed their old feathers. They molt in the fall and have a 
partial molt in the spring b7-eeding-season. They acquire a new set 
of feathers from the follicles. Some also shed parts of their claws, 
bill and bill membranes. (Figure 200.) 

^ For further data on temperature and color, see Knowlton's Birds of the World. 



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Color. — (i) The chemical absorption colors have coloring matter 
as a pigment or coloring solution. Colors thus produced are black, 
red, brown, orange and yellow, rarely green, and never blue. Certain 
red birds (plantain eaters, Miisophagidae) lose their red color in the 
rain but regain it when dry. The pigment (turacin, a copper salt) 
stains the water into which the animal goes for a bath. 




Fig. 199. Forms of beaks. After Claus. Forms of beaks {a, b, c, d, k, after 
Naumann; g, i, m, 0, regne animal; /, from Brehm): a, Phoenicopterus antiquorum; b, 
Platalea leucorodia; c, Emberiza citrinella; d, Turdiis cyaniis; e, Falco candicans; f, 
Mergus merganser; g, Pelecanus perspicillatus; h, Recurvirostra avocetta; i, Rhynchops 
nigra; k, Columba livia; /, Balaeniceps rex; m, Anastomos coromandelianus; n, Ptero- 
glossus discolor; 0, Mycteria senegalensis; p, Fakinellies ignetis; q, Cypselus apus. 
(From Daugherty. Courtesy of W. B. Saunders & Co.) 



(2) Another type of color production is by means of pigment 
combined with structural peculiarities, such as ridges and furrows 
in the surface of the feather itself. Thus we find produced blue, 
green usually, sometimes yellow. In transmitted light, feathers 
with these colors show the color of the pigment. 

(3) Metallic colors are found in the humming birds, dove, grackle, 
starling, and peacock. The commonly accepted hypothesis is that 



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357 



77ietallic colors are due to the structure of the surface of certain parts 
of the feathers such as striae^ ridges, knobs or pits, in combination 
often with an extremely colorless layer, these elements acting as 
prisms. Dr. R. M, Strong believes that in the pigeon the metallic 
colors of the neck feathers are due to spherical granules of the trans- 
parent wall and terms them " plate interference colors " or New- 
tonian rings. Feathers are found only on certain feather tracts 
which differ in different species of birds. 




Fig. 200. Foot forms, a, semi-palmate, wading of Ciconia; b, perching of Turdus; 
c, rasorial of Phasianus; d, raptorial of Falco; e, adherent of Cypselus; f, cursorial of 
Struthio; g, zygodactyl (scansorial) of Picus; h, lobate of Podiceps; i, lobate and 
scalloped of Fulica; k, palmate of Anas; I, totipalmate oi Phaethon. (From Schmarda. 
Hertwig-Kingsley. Courtesy of Henry Holt & Co.) 

Skeleton. — The forelimbs and pectoral girdle (Figure 201) are 
modified for flight. The skeleton of the limb is rigid. The hind 
limbs and pelvic girdle are used for bipedal locomotion. The 
skeleton is permeated by air usually in ratio to the mode of life. 

(i) Condors and cranes, soaring birds, have lightly built skele- 
tons. (The snipe and the curlew have airless bones, but fly long 
distances.) 

(2) Ducks and other water fowls have cavities of the long bones 
filled with marrow. 



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Fig. 20I. Skeleton of an Egyptian vulture. Rh, cervical ribs; Du, inferior 
spinous process of the thoracic vertebrae; CI, clavicle; Co, coracoid; Sc, scapula; St, 
sternum; Stc, sternocostal bones (sternal ribs); Pu, uncinate process of the thoracic 
ribs; % ilium; Js, ischium; P^, pubis; H, humerus; R, radius; U, ulna; C C, carpus; 
Mc, metacarpus; P' P" P'", phalanges of the three fingers; Fe, femur; T, tibia; F, 
fibula; Tm, tarso-metatarsus; Z, toes. (Claus-Sedgwick. Courtesy of Macmillan and 
Co., Ltd.) 



AVES 359 

(3) Bones of strictly aquatic birds are solid, being filled with 
bony tissue. The presence of air in the bones is believed to aid in 
oxygenizing the blood and in adjusting the air pressure when a bird 
descends rapidly from a great height. 

A fossilized wing of a pterosaur recently sent to the U. S. National 
Museum from Oregon was so perfectly preserved that it was possible 
to determine the character of the bones. Instead of being hollow 
as in our modern fliers, the cavities of the bones were filled with light 
spongy tissue which served to strengthen them. 

Digestive System. — The mouth is without teeth. (Vestigial 
teeth are present in some parrots.) The tongue is of various types: 
(i) Pointed, in the pigeon; (2) Long and protrusible, in the wood- 
pecker; (3) Short, in parrots; (4) Sucking tubes, in the humming 
birds. 

In birds we find that swallowing consists of violently jerking the 
head with an accompanying tongue pressure. There is no soft 
palate, and no epiglottis is present, but the larynx is protected by 
retroverted papillae at the base of the tongue. Insectivorous birds 
have a pouch at the base of the throat. In the nutcrackers there is 
a goitrous swelling in the throat, where the animal stuffs itself with 
nuts. The pelican's enormous bill holds 10 quarts of water. 

The upper part of the esophagus has buccal glands, sometimes 
called salivary glands, used to moisten the food. The crop is a non- 
glandular sac in which the food is softened and macerated. Animal 
food may remain in the crop for 8 hours, and vegetable food may be 
retained for from 16 to 20 hours. Fruit and insect eating birds 
have no crop. The pigeon has a double crop. " Pigeon's milk " is 
formed in the o'op and consists of proteins and oil, with no casein 
and no sugar of milk. It is a milky appearing fluid which mixes 
with macerating grains and is regurgitated for the young. The 
toucan regurgitates and chews over its food. The indigestible parts 
of the prey of the owl are regularly " cast " or regurgitated from the 
stomach. The lower part of the esophagus is a continuation from 
the crop to the stomach. The proventriculus has glandular walls, 
its gastric follicles secreting gastric juice. (Figure 202.) 

The gizzard is thick and muscular, and is used to grind food. 
It corresponds to the pyloric end of the mammalian stomach. 

The triturating agents are hard foreign bodies such as sand and 
gravel. Pigeons and other gallinaceous birds carry gravel to their 
young. It is necessary to have such in order to bruise the grains 



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and allow the gastric juice to act. Fowls can pulverize glass and 
some metals by grinding them in the gizzard. 

The small intestine consists of the duodenum and the ileum. 



Esophagus (upper portion) 
Crop 




Esophagus C/oiver portion) 



Liver Co small portion) 

Bile ductus 
■Fttncreos 
Proventricu/us 



Gizzard 

Spleen 

Ceca 
■Duodenal loop 






Recturf) 



Anus 



Fig. 202. Digestive tract of common fowl. (Drawn by W. J. Moore.) 



The duodenum has a U-shaped loop. This varies in different birds 
but is ordinarily quite long and equal to twice the length of the body, 
except in the fish eaters, where it may be but one-eighth the length 



AVES 361 

of the body. The ileum is not ordinarily long, but in the owls it is 
nearly as long as the duodenum. 

The rectal ceca are diverticula at the point where the ileum 
enters the rectum. In the grebe, a single cecum in present. In 
most birds there are two ceca, variable in length according to their 
habits. In the pigeon the ceca are not more than 2 inches long 
(shorter than in any other vegetable feeder) while in the common 
domestic fowl, they may reach a length of 3 feet. 

Rectum. — The large intestine (called the rectum rather than the 
colon) is wider than the small intestine, and has coarse, short villi. 
It terminates by a valvular opening in a dilated cavity, the remains 
of the allantois (see page 302), now a rudimentary urinary bladder. 
The ureters and generative ducts open into a transverse groove at 
the lower part of the urinary dilation. The anal follicles are in a 
conical glandular cavity communicating with the posterior part of 
the cloaca and named the " Bursa Fabricii." 

Liver and Gall Bladder. — There is usually a gall bladder, with 
two bile ducts leading from the large liver to the duodenum. The 
pigeon has no gall bladder but the fowl has an extremely large one. 

Pancreas. — The pancreas is a compact elongated reddish gland 
lying in the loop of the duodenum, into which it discharges its 
ferments through three ducts. The three enzymes digest proteins, 
carbohydrates and fats as in mammals (p. 432). 

Circulatory System. — The heart is comparatively large. (Figure 
203.) Two auricles are present and the two ventricles are com- 
pletely separated. The right auricles receive impure blood from 
the right and left precavals, and the postcaval veins. The blood 
passes from the right auricle through the auriculo-ventricular valve 
to the right ventricle. From the right ventricle it goes past the 
semilunar valves to the pulmonary artery and thence to the lungs. 
Four pulmonary veins from the lungs bring the blood to the left 
auricle. From the left auricle through the mitral valve it passes to 
the left ventricle. From the left ventricle it passes the semilunar 
valves to the right aortic arch ^ which gives off the innominate 
arteries, then continues as a dorsal aorta. Venous and arterial 
blood do not mix in the bird. The jugular veins are united by a 

8 In the reptiles, the right aorta transmits pure blood, while the left aortic arch 
contains mixed blood. 

The pigeon (Columba) has about 2,000,000 red corpuscles in a cu. mm. of blood. 
Erythrocytes vary in size from 12.1 microns in the fowl to 14.7 in the pigeon. 



362 



AVES 



transverse vein so that if the head is turned around the blood can 
still flow back into the heart through one of the jugular veins. 



Grac/iiol artery 

Srochio/ t^e/n 

Subclavian artery 




Vertebral vein 
Vertebral artery 

■Juqulor vein 

Common carofi'd artery 

Brachial artery. 

Broctiia/ vein 

.Lett pectorof 
arteries and veins 



__Internal mammary 
artery and vein 

— Left auricle -. 



- J f 

Rii^tlt precavat vein y / 
Aortic arch 
flight auricle 
Post cava/ vein — 

Riqtit ventricle "^ 

Hepatic veins 

Reno/ artery 
temorot artery 

Afferent renal vein-^^=-^=S 

t^emorol vein 

Ffenal porta/ vein 

3ciafic artery 
Renal arteries 

Dorsal aorta 

Fig. 203. Heart of pigeon. (After Parker's Zootomy. Courtesy of Macmillan and 

Co., Ltd.) 



"^Left pulmonary artery 
Left ventricle 

—Coe/ioc artery 
Dorso/ aorta 
-Anterior mesenter/c artery 

■Epiijastric vein 

I/iac vein 

Afferent renai vein 

—f^emora/ artery 

Femora/ vein 
Renal vein 



Respiratory System. — Air passes from the anterior nares or 
nostrils through the posterior nares, pharynx, trachea, and bronchi 
into the lungs and thence into from six to nine large air sacs. The 
air is forced into the air sacs by passage through the air in flight 
and out of them by wing compression. Hollow bones which render 
them lighter in the air are found in the soaring birds. 

Voice Box. — The syrinx is a structure found at the point where 
the trachea divides into the bronchi. A flexible valve extends 



AVES 363 

forward at the point where the trachea divides. Muscles control 
the tension of this valve and the number of vibrations and pitch 
resultant are thereby regulated. 

Bird Songs. — Call notes are heard throughout the year, but 
songs, which Darwin believed to be associated with sexual selection, 
are limited in most birds to the breeding season. (See page 515, 
Sexual Selection.) The rhea and the ostrich are said to be mute. 

References on Bird Songs 

Allan, F. H. Some little known songs of common birds. Nat. Hist., 

vol. 22, p. 235. 
Oldys, Henry. 191 7. The meaning of bird music. American Museum 

Journal, vol. 17, February, pp. 123-126. 
Saunders, Aretas A. Flight songs and mating songs. Auk, vol. 39, 

p. 172. 
Tyler, W. M. 1923. Courting orioles and blackbirds from the female 

bird's eyeview. Auk, vol. 40, Oct., pp. 696-697. 

Excretory System. — The kidneys are paired and ordinarily three 
lobed. The first lobe is usually larger although in the pelican the 
third lobe is larger. The tern has 7 or 8 lobes in its kidneys and the 
eagle has four. No urinary bladder is present. A rudimentary 
urinary bladder is found most highly developed in the ostrich, while 
the owl, pelican, grebe and swan have small ones. The urine 
solidifies on reaching the air.'' The adrenals (suprarenals), endo- 
secretory glands regulating blood pressure, are rounded and yellow- 
ish and found on the inner edge of the first lobe of the kidney. 

Reproductive System. Male. — In the male, there are two testes 
which vary greatly in size according to season. Two seminal 
vesicles store the sperms. There are two vasa deferentia with 
eversible papillae at the cloacal end. The Anatidae have a penis, 
coiled when flaccid. The Cursores have a penis consisting of two 
fibrous bodies with a fissure between. (Figures 204 and 205.) 

Female. — In the female the right ovary is degenerated^ with a 
vestigial oviduct. The left ovary persists and has a long convoluted 
oviduct with a papilla at the end. The oviduct secretes albumen 
in the upper part, farther down the shell gland secretes the shell 
membrane and finally the posterior part secretes the shell. The 

^ Great deposits of the feces and urine of certain birds are found in Peru. This 
substance, rich in salts, is sold as the fertilizer, "guano." See page 368. 



364 



AVES 



uterus Is considerably enlarged. Antiperistalsis of the oviduct 
sometimes results in the formation of a new shell on an egg already 
provided with one. 



Ovory - with 

ot/o of different siie 



■Funnel of oviduct 




•Kidney 



-Oviduct 



Ureter 

Sfiell glared 

-Rudimentary ritjflf 
ov/duct 
Vesicula s&niinolts \ \ \\ jl / / 

Openinq of the areter\ \ \\ \\ / y^ Opening of ureter- 

into tfie cloaca NsV'O^^^— ^5^/^ '"'" ''^^ clooca 

Open.no of vas deferensfii^^ ^'^^ Opening of oviduct 

,nto the clooca / ( j 1 ,„^„ ,^g cloaca 

-Cloaca ^-Cr^ ~Z^^ 

Cloaco 

Fig. 204. Reproductive system of the Fig. 205. Reproductive system of the 
fowl, male. (Drawn by W. J. Moore.) fowl, female. (Drawn by W. J. Moore.) 

Nervous System. — The brain is short and very broad. The 
cerebral hemispheres are large and the optic lobes immense. The 
cerebellum is extremely large, indicating well-developed equilibration. 
The olfactory lobes are very small. 

Sense Organs. — The bill and tongue are tactile organs; tactile 
nerves are also present at the base of the feathers, especially the 
wings and tail. The sense of synell is very poorly developed while 
the sense of taste is poor but serviceable. Hearing is extremely 
acute and vision is phenomenal. The eyes are very large and of a 
biconvex shape. Birds have a tremendously developed power of 
accommodation. They can swoop down to the water with great 



AVES 2^s 

rapidity and seize a fish which is unseen by a man standing on a clifF 
above the water. Buzzards see a sleeping man and gather quickly. 
Many a traveler has when ill been quite disconcerted by the sight 
of buzzards gathered in his vicinity. Keen eyes enabled one of them 
to note his quietude and others quickly gathered as the scout circled 
downward. Whether the buzzard smells decaying flesh of dead 
animals is a debated question. Experiments seem to indicate that 
it sometimes does. Many zoologists are of the opinion that sight 
Is the chief means of locating the buzzards' food. 

Susceptibility of Birds to Poison.— Small doses of morphine 
produce in birds disturbances of the digestive tract and a light sleep. 

Types of Nests. — Birds' nests vary greatly in structure and in 
location. Birds may deposit their eggs on the sand, unprotected, 
or they may build a nest in an excavation in the ground or in a 
hollow tree. Some forms seek out lofty eyries^ others build colonies 
on the sides of cliffs, while still others build mounds. The mound- 
building birds of Australia open the mounds to admit the sun and 
remove or add debris as the humidity varies. The nests of others 
float on stagnant pools or are built in the grasses of swamps and 
meadows. 

There is a great specialization in the material \x^Q.di in constructing 
the nest. Some warblers line their nests with the seed capsules of a 
certain species of moss. The tailor bird sews leaves together with 
plant fibers. The tropical bower-bird includes bits of shell and bone 
in its nest. The crow and the starling are particularly fond of bright 
bits of metal. Stories are told of tame crows that successfully stole 
table silver. 

The chipping sparrow lines its nest with horsehair., while the 
crested flycatcher usually Includes a portion of the cast skin of a snake. 
As mentioned before, the South American hornbill male seals his 
spouse Into her nest in a hollow tree and brings food to her during 
the nesting period. The chimney swift builds its nest (In a chimney) 
of twigs stuck together by saliva. 

The edible birds' nests of the Orient are built by swift-like birds 
{Collocalia) , in rocky caverns along the sea. The first nests built 
are made up almost entirely of glutinous salivary secretion and are 
sold for as much as $15.00 per pound. The first quality nests are 
almost entirely destroyed by native collectors. Later nests con- 
taining twigs and other foreign matter are not destroyed, or the 
birds would soon be extinct. 



266 AVES 

One of the most beautiful of the birds' nests is that of the Balti- 
more oriole. It is easily recognized by the long strand suspending it 
a foot from its supporting branch. It is tightly woven and when the 
bird is on its nest its weight closes the opening so that no rain can 
enter. The South American cacique builds a nest similar to that of 
the oriole and with a much longer anchor. It may hang seven feet 
from a branch. 

Bird Migration. — Coward classifies birds with respect to their 
migrations as: 

(i) Permanent residents; (2) Summer residents. (Leaving in autumn 
and returning in spring); (3) Winter residents. (Leaving in the spring 
for their breeding area); (4) Birds of passage — or spring and autumn 
migrants; (5) Irregular migrants — occasional invaders; (6) Stragglers or 
wanderers. 

The American Golden plover nests along the Arctic coast from 
Alaska to Hudson Bay; winters in Argentina, after a roundabout 
oceanic flight of 2,500 miles, passing through Labrador and Nova 
Scotia with rests and feeding at each of these places, then flies 
directly across the sea to Guiana and thence after a further rest to 
Brazil where it feeds until March. The return route is a more 
direct one. The distance covered in the elliptical indirect route is 
said to be nearly 20,000 miles. Birds usually migrate in company 
with other experienced travellers, but they make successful pil- 
grimages when it is evident that older birds are not there to guide 
the flock. 

Storks marked in Prussia have been taken in the African Trans- 
vaal. The Arctic tern nests along the coast of Maine and North- 
ward to the limit of land, but winters along the borders of the Ant- 
arctic continent. Thus it migrates about 11,000 miles, probably at 
sea. Cooke states that the Arctic tern has more hours of daylight 
than any other animal. " The midnight sun has already appeared 
before the birds' arrival at the Northern nesting site, and does not 
set during their entire stay at the breeding grounds. During two 
months of their sojurn in the Antarctic^ the birds do not see a sunset." 
They have 24 hours of daylight for at least 8 months of the year. 

Some species fly by day and some by night, others fly both day 
and night. Some day-migrants follow coast lines or river valleys, 
guiding themselves by sight. But in the case of the noddy and sooty 
terns, studied by Watson and Lashley, birds liberated at sea, 600 



AVES 367 

miles from their nests and 450 miles from shore, and others liberated 
on the mainland 850 miles away flew directly to the proper island 
and nests. 

Why Birds Migrate. — One of the commonly accepted theories as 
to migration is that ages ago the United States and Canada were 
occupied by non-mi gj-ato7j birds. When the Arctic ice fields moved 
South during the glacial period, rendering the Northern half of the 
continent uninhabitable, because of lack of food supply and a low 
temperature, the birds migrated farther and farther each decade 
until finally the racial habit of long migrations was established. 
Another theory is that the birds' original home was in the South and 
that as the ice retreated northward they sought a less crowded 
breeding ground, only to return to their winter quarters in the South. 

In some recent work done by W. Rowan of Alberta, Canada, the 
factor of the physiological impelling force of the developing gonads 
is emphasized along with the environmental factor provided by 
varying day lengths.'^ Rowan says: " Migration cannot be looked 
upon as an act of volition, but as the automatic response to a certain 
physiological state probably induced by a gonadial hormone. The 
birds must migrate if physically able to do so." Unquestionably 
Rowan's point regarding the influence of the gonads is well taken. 
(See Fish Migration, page 263.) 

We know that birds have a time sense, and that the northerly 
movement of the robin is correlated with the attainment of a certain 
mean daily temperature. The average of weather conditions 
influences the average time of arrival, and the flight of night mi- 
grants is known to be correlated closely with meteorological condi- 
tions. Adams found that bird migrants arrive in waves following 
peculiar types of weather. 

In spite of the evidence collected by many observers, there are 
those who seem content, like many of the adherents of the " parent- 
stream " theory in fishes, to dismiss the whole problem by stating 
that it is probably due to a mysterious sense of direction. 

Others have suggested that a peculiar physical property of the 
feathers causes the magnetic pole to exert a powerful attractive 
influence. 

* In his studies on the sexual cycle of the European starling, Bissonnette has shown 
that increased daily light periods will increase spermatogenic activity. Consult 
Bissonnette, T. H., 1931 (Jour. Exp. Zool., vol. 58, pp. 281-319), and earlier papers. 



368 AVES 

Speed of Flight. — Migrating birds are able to reach a speed of loo 
miles an hour and travel from i,ooo to 5,000 feet above the earth. 
A carrier pigeon is recorded as having averaged fifty-five miles an 
hour for four hours, probably exceeding the speed of most migrants. 

Mr. Thomas Ross, who is in charge of the army lofts at Fort 
Monmouth, N. J., is quoted (American Magazine, June 1928) as 
stating that an American carrier pigeon flew 300 miles at a little 
over seventy-one miles an hour. He also quotes the unsubstan- 
tiated statement that a pin-tail duck has made 125 miles an hour. 
Herons, hawks and flickers fly about twenty-five miles per hour. 
According to Chapman, the great wandering albatross of the South- 
ern Seas has been known to fly 3,400 miles in eight days. 

Economic Importance of Birds. Positive. — i. The eggs and 
flesh of the common fowl, ducks, geese, and even the ostrich, are 
eaten. 

1. Feathers of the ostrich, the egret and the bird of paradise 
have been in times past great favorites for ornamentation. 

3. The Chinese are extremely fond of the edible birds' nests 
secured along the coast, north of Borneo. 

4. From the Islands of the South Pacific comes the important 
fertilizer known as guano. ^ This has been deposited for centuries. 

5. As scavengers, the buzzards and vultures are especially 
valuable. 

6. Birds are preeminently our best friends in that they destroy 
insects, rodents and the seeds of our most pestiferous weeds. The 
English starling, until recently considered as great a pest as the 
English sparrow, is, according to S. S. Pennock of Philadelphia, an 
extremely successful hunter of the larvae of the Japanese beetle. 

Negative. — i. Destroyers of poultry. Very few birds attack 
domestic fowls. Several species of the hawks may be classed as 
injurious, while the only owl that is injurious is the great horned owl. 

2. Enemies of beneficial birds. The English sparrow, the 
starling and the jay drive away other birds and the jay eats eggs 
and young. The shrike or butcher bird is an important enemy of 
our bird friends. 

3. Destroyers of crops and fruits. The crow, the English spar- 
row, the robin, and the grackle consume some of our food products. 

' For further information regarding guano, consult: Murphy, R. C. 1924. The 
most valuable bird in the world. Nat. Geog. Mag., vol. 46, p. 279, and Coker, R. E. 
1920. Peru's wealth producing birds. Nat. Geog. Mag., vol. 37, pp. 537-566. 



AVES 369 

4. Disseminators of injurious seeds and parasitic animals. 
Even our valuable game birds may be the means of dispersing 
parasitic worms and protozoa, and it is a well-known fact that the 
starling, introduced into New Zealand, spread the seeds of the 
English blackberry, with the result that the thorny bushes form a 
snare for lambs and interfere with cultivation. 

References on Birds 

Beal, F. E. L. and Others. 1916. Common Birds of S. E. United 

States in Relation to Agriculture. Farmers' Bull. no. 755, U. S. 

Dept. Agr. 
Bradley, O. C. 1915. The Structure of the Fowl. A. and C. Black, 

Ltd., London. 
Chapman, F. M. 1910. Birds of Eastern North America. New York. 
Chapman, F. M. 1903. Color Key to North American Birds. New 

York. 
Fisher, A. K. 1908. Economic Value of Predaceous Birds and Mam- 
mals. Yearbook of the U. S. Dept. Agr. 
FoRBUSH, E. H. Game Birds, Wild-Fowl and Shore Birds. Mass. 

State Board of Agriculture. 
FoRBUSH, E. H. Useful Birds and their Protection. Published by the 

Massachusetts State Board of Agriculture. 
Friedmann, H. 1929. The Cow Birds. C. C. Thomas Co., Springfield, 

111. 
Heilmann, G. 1927. The Origin of Birds. D. Appleton and Co., New 

York. 
Henshaw, H. W. Fifty Common Birds of Farm and Orchard. 

Farmers' Bull. no. 513. 
Kaupp, B. F. 1 91 8. The Anatomy of the Domestic Fowl. W. B. 

Saunders Co. 
McAtee, W. L., and Beal, F. E. L. Some Common Game, Aquatic, 

and Rapacious Birds in Relation to Man. Farmers' Bull. no. 497. 
Mentor. 1913. Game Birds of America. Vol. i, Oct. 6, no. 34. 
Mentor. 1916. American Birds of Beauty. Vol. i, June 2, no. 16. 
National Geog. Mag. 1914. 64 Pictures in Colors of Common Birds 

of Town and Country. Vol. 25, May. 
Thomson, J. A. 1923. The Biology of Birds. The Macmillan Co., 

N. Y. 
Weed, C. M., and Dearborn, N. Birds in their Relation to Man. 

J. B. Lippincott Co., Philadelphia, Pa. 



37° 



AVES 



Fossil Relatives of the Birds. Saururae. — These reptile-like 
forms had a long, slender, lizard-like tail, sharp teeth, a short neck, 
a small keel to the breast bone and claws on the fingers and toes. 
Two specimens were found in the Jurassic of Bavaria. The 
Archeopteryx (Gr. ancient wing) was discovered in 1861 at Solen- 




FiG. 206. Archeopteryx as it would appear with feathers restored. (From Romanes, 
Darwin and After Darwin. Courtesy of Open Court Publishing Co.) 

hofen, Bavaria; (Figure 206.) It had been so well preserved be- 
tween the layers of lithographic slate that the details of feathers of 
the wing and tail were plainly seen. It had a bird-like head and 
brain. Its jaws were, however, equipped with sharp reptilian teeth. 
The head and neck were devoid of feathers while the legs had quill 
feathers. The wings had three fingers with reptile-like claws, with 



AVES 



371 



the metacarpal bones separated. The fingers had the same number 
of joints as in the lizards. The keel was only lightly developed. 
Archeopteryx used its wings chiefly for planing rather th.B.n flying. 
The Archeornis (Gr. ancient bird), slightly different from the Arche- 
opteryx, was discovered in an almost perfect state of preservation 
in 1877, "6^^ Eichstatt, Bavaria. It had an extremely long reptilian 
tail with twenty-one joints, which was " Hke a telescope pulled out, 
while the tails of the modern birds are like a closed telescope." 




Fig. 207. Left, Ichthyornis victor. Right, Hesperomis regalis. (From Daugherty. 

Courtesy of W. B. Saunders & Co.) 

Ichthyornithiformes. — Ichthyornis (Figure 207 A) had socketed 
teeth, a keeled sternum and was a strong flyer and apparently a fish 
eater. It was found in the Cretaceous of Kansas. It was small, 
about the size of a pigeon. 

Hesperornithiformes. — Hespej-ornis (Figure 207 B) was a three- 
foot, flightless diving bird, with grooved teeth, a keelless sternum 
and strong paddle-like hind limbs. It was also found in the Creta- 
ceous of Kansas. 

A Living, Connecting Type. — In the South American Hoactzin, 
the adults are like certain pheasants, but differ in anatomical 
characteristics. The breast bone is wider behind than in front; the 
keel of the sternum is confined to the posterior part; the crop is 



372 



AVES 



large and muscular, taking the space usually filled with pectoral 
muscles and the anterior part of the sternum. The young birds 
when first hatched have a clawed thumb and index finger on the wing, 



Nucleus of ^ 

Pander 



l-otebra-^ 



Blastoderm 

,. NecK of iQtebra 




Inner- She/I 

Outer- £helf 
membrane 



White yolk--' 
yel/ow YolH 



■-CholQZO 



Dense a/bumen 



'' l^e.ss dense a/bumen 
^ Vitellines membr-ane 



Fig. 208. Diagram of the hen's egg in longitudinal section. (After Lillie. Courtesy 

of Henry Holt & Co.) 



resembling the condition in Archeopteryx. They are able to climb 
about the branches and find their own food, using their feet and wing 
digits. 



fhoryn^eof poucnes I to JOT 



Anr. carc//na/ v. 
Aortic Qr-dh JS"-, 

Aortic ortzriei 
TTandlZI 

Trocnsa 

/\trium - 

Duct Of Cuvier •- 



Stnus s/enosus ' 

i- iver - 
Ventricle- 



Dorsal aorta 
Mesonephros ' 
F<ost. cardinal 
Hind 



Aortic arch I 

(disopfieorln^) 



carotid o . 



Ext. iliac 
CI 




EKt. carotid a. 



-Ant. card /not v. 



Allantoic vein 
Yolk stocK 
Omph. mes. v. 
Ornpti. mes. a. 

Allonf-oic vein 

A //onto is 



Allantoic artery 
Proc todoe am 

Post-anal <jut 



Fig. 209. Internal organs of a four-day chick. (From Lillie, Development of the Chick. 

Courtesy of Henry Holt & Co.) 



CHAPTER XIX 



Mammalia 



Perhaps our chief interest in the Mammals is derived from the 
fact that we ourselves belong to this great class of vertebrates. In 
the early days man found his most formidable enemies among the 
mammals, and even now he suffers from the activities of the rodents. 
On the other hand, mammals have furnished milk, meat, and furs, 
and certain forms have been used for centuries as servants and 
beasts of burden. Like the Birds, they are a tremendous economic 
factor in our civilization. 

Characteristics 

Mammals have a double occipital condyle, a hairy skin, and well- 
developed milk glands. They are warm blooded, with the heart 
divided into four chambers and the single (left) aortic arch curving 
over the left bronchus and continuing as a dorsal aorta, the visceral 
arches modified into the earbones, with the cerebral hemispheres 
usually connected by a heavy commissure called a corpus callosum. 
The thoracic and abdominal cavities are separated by a muscular 
diaphragm. 

Order i. Monotremata. — This order includes egg-laying mam- 
mals with mammary glands devoid of teats. Eggs about half an 
inch long, rich in yolk with soft, but tough shells. Episternum and 
coracoid well developed. Oviducts distinct throughout; cloaca in 
both sexes, into which the ureters and urinary bladder open sepa- 
rately. In the center of the vertebrae the epiphyses are absent or 
imperfectly developed. The bones of the skull coalesce early. 
The corpus callosum is absent. (Figure 210.) 

The spiny ant eater {Echidna aculeata), found in Australia, 
Tasmania and New Guinea, reaches a length of about 18 inches. 
As the name would indicate, it is covered with spines and hairs. 
It curls up like a hedgehog when alarmed. It has no teeth but is 
provided with a long extensible tongue which it utilizes in securing 
insects and worms. It places its egg in a primitive mammary pouch 
consisting of a fold of the abdominal skin. The young when hatched 

373 



374 



MAMMALIA 



are fed by milk exuding upon the hairs of the mother's abdomen. 
The young are later protected by being concealed in a burrow. 
The long-snouted Echidna {Praechidna) is found in New Guinea; 
here under the name of the " Nodiak " it is eaten by the natives. 
The duck-bill {Ornithorynchus {paradoxus) anatinus) (Figure 2ii) 
is found in Australia, New Guinea, and Tasmania. It has a small 
rounded head, and a black horny bill. It crushes its food between 




Fig. 2IO. Echidna. (Courtesy of N. Y. Zool. Soc.) 

the ridged plates of its lower jaw and the roof of its mouth. Highly 
developed glandular cheek pouches aid in digesting the food before 
it reaches the small stomach.^ The body temperature of the duck- 
mole, like that of Echidna, is but two to five degrees higher than the 
surrounding medium. Its oviducts open separately into the cloaca, 
but as in the birds the left ovary and oviduct alone are functional. 
Aquatic, it digs burrows thirty feet into the banks of deep pools. 
It builds a nest and deposits two eggs. When hatched, the young are 
blind, hairless, with short beaks, but possessing teeth. The duck- 
bill has no mammae and the milk oozes out through many fine 

* Consult H. Burrel. 1927. The Platypus. Angus and Robertson Ltd., Sydney, 
Australia. 



MAMMALIA 



375 



apertures upon two mammary areas each about one half inch in 
diameter. The young scrape and suck the milk from these areas. 

Young duck-bills feed upon Crustacea, insects and worms. On 
each hind foot, male duck-bills, or duck-moles, have a sharp horny 
spur with a poison gland connected. 




Fig. 211. Platypus. (Courtesy of N. Y. Zool. Soc.) 



Fossil Relatives of the Monotremata. — Monotremata are found 
in the Pleistocene, and it is possible that the doubtfully mammalian 
types of Protodonta, Dromatherium and Micronodon^ of the Upper 
Triassic, are also related. 

Order 2. Marsupialia. — Viviparous, usually carrying their 
young (born in a rudimentary condition) in a marsupium or pouch; 
allantoic placenta usually absent. Small eggs undergo a total 
segmentation in most species, and develop in the maternal uterus, 
nourished by a secretion from its walls. The ventral surface 
is supported by the marsupial bones, slender rods articulated right 
and left, at the pubic symphysis. Corpus. callosum absent. 



376 MAMMALIA 

The opossum family {Didelphidae) ^ found in America, is dis- 
tinguished by the presence of a marsupial pouch. This may be 
absent or relatively shallow as in the case of some species or it may 
approach the highly developed condition existent in the kangaroo. 
The young of the Virginia Opossum {Didelphys virginiana) remain 
for two months with their mother, at first residing in the pouch, 
then ride around on her back. The opossum feeds on wild fruit, 
berries, corn, insect larvae, eggs and young birds and mammals. 

Tasmanian marsupials (Family Dasyuridae) have fewer incisor 
teeth than the American opossum; they lack a cecum and their tail 
is not prehensile. 

The Murine opossum, a mouse-like form, is found in South 
America. It is about the size of a chipmunk and lacks an abdominal 
pouch. 

The Australian ant-eater lacks a pouch and resembles a red 
squirrel in appearance. The wombats are unwieldy creatures 
resembling the badger. They have rudimentary cheek-pouches and 
tail. 

The Kangaroos {Macropodidae) are found in Australia where 
nearly all land mammals are marsupials. Unlike the opossum and 
the Tasmanian devily the kangaroo family are all herbivorous. The 
newly born young are taken by the mother and placed in her pouch 
where they remain until their eyes open and they have developed 
hair. For some time after this they return to the pouch from little 
excursions into the world. When first born, a kangaroo may be 
not more than an inch long. 

The " Old man " or gray kangaroo reaches a height of over five 
feet, weighs two hundred pounds and can leap over twenty feet, 
using its long legs and powerful tail. The red kangaroo with a brick 
red coat of a very fine, silky texture is the one most frequently seen 
in captivity. It reaches a height of almost four feet. The rock 
wallabies (genus Petrogale) do not utilize their tails a great deal in 
locomotion but use them as balancers. The black-tailed wallaby 
and the opossum are said to have starved out the other animals on 
Kawau Island. 

Fossil Relatives of the Marsupialia. — For the most part the 
marsupials are found as fossils from the Upper Triassic to the 
present. 

Order 3. Insectivora. — Small, usually terrestrial (but some- 
times aquatic or arboreal) clawed mammals; feet plantigrade. 



MAMMALIA 377 

generally pentadactyle; molars enamelled, tuberculated, and rooted. 
They have a primitive brain. There are frequently scales on the 
tail among the hairs; the clavicle is present; the animals have soft 
hair, and usually a proboscis-like, tactile snout. 

Feeding almost wholly on insects and worms they are chiefly 
nocturnal. They are found almost everywhere except in Australia 
and South America. Evidence from fossils indicates that they are 
survivors of extremely primitive placental mammals. The eyes are 
extremely small and in some cases hidden by fur. 

The colugo {kaguan) is a peculiar form, sometimes called the 
" flying lemur." It is found in trees from Siam to Java with a 
smaller relative inhabiting the Philippines. It belongs to a sub- 
order, Dermoptera. Extensions of its furry skin stretched between 
the fore and hind legs enable it to plane through the air like a flying 
squirrel. It is about the size of a small cat. 

The shrews {Soricidae) are small, mouse-like animals with 
pointed heads, external ears and eyes, rat-like feet, slender bodies 
and a short tail. The common shrew is found on the Atlantic 
coast, ranging from New England, Southward to North Carolina 
and Northwestward to Alaska. It is quick of hearing, utterly 
untameable, and from glands in the axillary region, emits a musky 
odor, which repels hawks, cats and foxes, but apparently attracts 
weasels and owls. The water shrew is the largest of the American 
forms, measuring 6 inches in length, with a tail over 2 inches long. 
The great musk shrew of India, called the " muskrat " in the Old 
World, is important as a destroyer of insect vermin. Some of the 
long-nosed shrews are aquatic, living in bank burrows and swimming 
and diving with ease. (Figure 212.) 

The short-tailed or " little " shrew {Cryptotis parvd) has a total 
length of but 3.1 inches and is the smallest American mammal. It 
is found from the middle West to the Atlantic coast. ^ Shrews eat 
worms, insects, young birds, but also feed on roots and nuts. Euro- 
pean superstitions regarding the shrews include such statements 
as that of Rev. Edward Topsell, who in his rare " Historic of Four- 
footed Beastes," printed in London in 1607, says of the shrew that 
" It is a ravening beaste, feigning itself gentle and tame, but, being 
touched, it biteth deeply and poysoneth deadly. It beareth a cruel 
minde, desiring to hurt anything, neither is there any creature that 

2 H. E. Anthony. 1928. Field Book of North American Mammals. G. P. 
Putnam's Sons, N. Y. 



378 



MAMMALIA 



it loveth, or it loveth him, because it is feared of all." (Ingersoll, 

1906 p. 71.) 

Physicians report the characteristics of the shrew as occurring 
in certain women and men as well. Perhaps dementia praecox and 
paranoiac tendencies may be fostered by a policy of letting children 
have their own sweet will, and only defending oneself from their 
actual blows. 




Fig. 212. Smoky shrew. (Courtesy of W. Va. Exp. Sta.) 



The moles ( Talpidae) have vestigial eyes, broad, spade-like front 
teeth and no neck. Unlike the shrew, the animals have no external 
ears or external eyes. There are twelve species. On the body the 
mole has fine, thick velvety fur, but the tail is hairless. 

The common mole is gray in color, with webbed hind feet, and 
reaches a length of about six inches. It burrows in loose earth and 
in ten seconds will leave upheaved tunnels. Hornaday timed a 
mole in a clover field and found that it had tunnelled twenty-three 
feet in seven hours. 

The star-nosed mole has, on the tip of its nose, eighteen ray-like 
points, with four smaller ones between them. It burrows into 
swamps along the banks of ponds and brooks and apparently is 
adapted to an aquatic life. It devours fish, fish eggs and water 
snakes and also feeds on insects and worms. 

The common European hedgehog has an armor of short, stiff, 
sharp gray spines which are not barbed as in the porcupine and which 



MAMMALIA 379 

are not discharged. When irritated, the hedgehog rolls itself into 
a ball with its head tucked between its feet. Hedgehogs feed on 
slugs and insects, but also eat small mammals and frogs, and are 
protected on account of their value as snake killers. Some Euro- 
peans are very fond of the flesh of the hedgehog. 

Fossil Relatives of the Insectivora. — The living families of 
moles, shrews and hedgehogs arose in the Eocene period. Related 
forms occurred in the Jurassic. R. C. Andrews has discovered in 
Mongolia fossil skulls with teeth of the insectivorous ty^pe, indicating 
the pattern from which insectivores, carnivores, and possibly pri- 
mates may have evolved. 

Order IV. Chiroptera. — Clawed animals with fore-limbs modi- 
fied for flight, the bones, especially those of the second to the fifth 
digits, being greatly elongated so as to support a broad web of skin 
extending back to the hind-limbs. The sternum has a keel for the 
attachment of the pectoral muscles, which are important to the 
movements of flight. The dentition is complete. The cerebral 
hemispheres are smooth and do not overlap the cerebellum. Anal 
glands, furnishing a strong, even offensive smelling secretion, are 
common. Although bats are swift fliers they do not have air spaces 
in their bones as do some of the birds. There are more than six 
hundred species of bats, which at first were classed with birds. 

The Megachiroptera are large, diurnal forms, sometimes called 
fruit bats, fox bats, or "" flying foxes." They destroy fruits and on 
this account have been barred from admission into some states. 
The larger fruit bats are eaten by the natives of the East Indies. 
The hammerheaded bat is found in Africa. 

The Microchiroptera include the leaf -nosed bats, the vampire bats 
and the smaller common forms. The leaf-nosed bat is found in 
California and Mexico and has a wedge-shaped leaf of naked skin 
just behind the nostrils. The javelin bat, ranging from South Amer- 
ica to Mexico, is a vampire or blood-sucker, attacking horses, cattle 
and men. It reaches a length of four inches. An extremely large 
form from South America, erroneously called the " great vampire," 
is not at all injurious, but feeds on fruits and nuts. It is twenty- 
eight inches in length. 

The naked bats of Borneo have thick leathery skins and a scent 
gland on their neck. Under each arm they have a mammary pouch 
in which the young are carried and nursed until they are able to fly. 

The cominon bats ( Vespertilionidae) are found all over the world. 



38o MAMMALIA 

Of the two hundred species, there are less than twenty in the United 

States. 

The commonest American species are the little brown bat {Myotis 
lucifngus) which is less than four inches in length, and the brown bat 
{Eptesicusfuscus) which is widely distributed throughout the United 
States. The little red bat is a swift flyer and as active as a bird. 
The gray bat is a large form reaching a length of three inches. It is 
found in the United States and Canada. The big-eared bat has ears 
half as long as its body and is found in the Southern States, 

One family {Molossidae) seems more like the rat, for it is ter- 
restrial. 

Fossil Relatives of the Chiroptera. — Bats are known from the 
Eocene of Colorado. 

Order V. Carnivora. — Clawed, furry mammals with at least 
four digits. Incisors small; canines large, curved and pointed; 
premolars and molars usually compressed; stomach simple, cecum 
small. Tapetum lucidum of eye very shiny. Clavicle lost or 
reduced, ulna and radius well developed. Teats abdominal, uterus 
bi-cornuate, placenta deciduate, usually zonary. 

Sub-Order Fissipedia. — The cat family (Felidae) includes lions, 
tigers, leopards, and the like. 

The " saber-tooth " cats were found in America and the Old 
World in the Tertiary period. The great " saber-tooth " tiger 
{Smilodon) was as large as our largest Kadiak bear. 

The puma, cougar or " mountain lion," an American form, once 
ranged over the whole continent. It may reach a length of seven 
feet and a weight of two hundred pounds. While it is stated that the 
puma dreads mankind there are well-authenticated reports of at- 
tacks on children and grown men. 

The jaguar is the largest and handsomest species of the cat 
family in America. It is found as far North as Southern Texas. 
It is an enemy of pigs, cattle, horses and wild mammals, but ap- 
parently afraid of man. It may reach a body length of five feet 
with a tail two feet long and weigh one hundred fifty pounds. (Figure 

2I3-) 

The ocelot or tiger cat, also found in Texas, is a small leopard, 
with horizontal black stripes on a yellowish ground color. It is 
about the size of a small spaniel and feeds on birds and arboreal 
mammals. 

The Canada lynx is a small bob-tailed wild cat found in Quebec 



MAMMALIA 



381 



and Ontario, but ranging southward into the United States. The 
Bay lynx, wild cat or bob-cat, is found east of the Mississippi in 
wooded areas, and extends westward to the Pacific coast states. It is 
a formidable enemy of cotton tail rabbits. 




Fig. 213. Jaguar. (Courtesy of N. Y. Zool. Soc.) 

The lion has been considered the king of beasts for centuries.^ 
Amenenhat I. recorded proudly, 2000 B.C., " I hunted the lion." 
The lion, explorers state, is by no means the bold animal that it is 
traditionally supposed to be. The African buffalo is said to be more 
than a match for a single lion. The zebra seems to be the lion's 
favorite food. (Figure 215.) 

The tigo- is found in Persia, Siberia and Manchuria and ranges 
southward through China and the Siamese and Malay Peninsula to 
Java, but is not found in Borneo. Passing around the Bay of Ben- 
gal, it has never crossed to Ceylon. It is considered a far more 
dangerous animal than the lion. In 1927, the Indian Government 
reported 1,033 persons killed by tigers. 

The leopard is a more active, sly animal than either the lion or 
the tiger, and is probably responsible for many more losses among 
sheep, cattle and ponies. Leopards killed 218 persons in India in 
1927. 

1 The Marcomanni called the lions sent across the Danube by the Romans "dogs." 
Herodotus II. 69. 



382 



MAMMALIA 



The cheeta or hunting leopard of Africa and India belongs to the 
genus {Cynaelurus) intermediate between the cat and the dog. It 
has been trained to capture game for its master in India. 

The cojnmon house cat has descended from the single wild species 
{Felis maniciilatd) of Northeastern Africa. Egyptians prepared 




Fig. 214. Canada lynx. (Photo by courtesy of Canadian National Railways.) 



mummies of cats which indicates that they regarded them as beloved 
companions. A tablet in the Berlin Museum dating from 1800 
B.C. is inscribed with the word, " mau," meaning cat. 

The Egyptian wild cat of today {Felis libyca) is about the size 
of the domestic cat, generally yellowish in color with faint pale 
stripes which become darker on the limbs. There are today about 



MAMMALIA 



3^3 



thirty races of cats, grouped into long-haired and short-haired 
varieties. There is also a Mexican hairless cat. (See p. 524.) 

The civets ( Viveridae) are relatively small animals with incom- 
pletely retractile claws. From their scent glands, " civet " perfume 
is secured. 




Fig. 215. Tsavo lions. Both specimens are males, but from an arid region of 
Africa where manes are lacking. They killed 135 men employed in the construction of 
the Uganda R. R. (Courtesy of Field Museum of Nat. Hist.) 

The mongoose ^ (mungoos) is found in Egypt where it is called the 
ichneumon and in East India where it goes by the native name, 
mungoos. It lives in thickets and in holes among rocks. It is an 
enemy of snakes, lizards, poultry and rodents and is said to oc- 
casionally chew the ears of native infants, left sleeping. 

There are three species o( hyenas {Hyenidae). They are found 
in Europe, Asia and Africa, where they are much despised. They 
are scavengers. They have a large dog-like head and strong jaws 
with thirty-four powerful conical teeth. Hyenas are able to kill 
donkeys, sheep and camels. 

The raccoons {Procyonidae) are plantigrade like the bear family. 
They are found in the wooded regions of the Southern and Eastern 
states, especially in swamps. They live in hollow trees and are 

3 In 1872 the mongoose was introduced into Jamaica to destroy the rats infesting 
the sugar cane. At first beneficial there, it began killing poultry until it proved a 
distinctly injurious form. Recently it has turned cannibal and relieved the situation. 



3^4 



MAMMALIA 



omnivorous. They have the peculiar habit of washing (soaking) 
food before eating it. 

The bears ( Ursidae) are plantigrade (flat-footed) animals with 
long claws that are not retractile. They are terrestrial and omniv- 
orous. Very few of them are able to climb trees. The polar bear 
has a pure white coat the year around. In the winter, it lives on 
fish, seals, walruses and the carcasses of whales, augmenting its 
diet in the summer by vegetable matter. It reaches a height of 
fifty inches and a length of over seven feet and may weigh over one 
thousand pounds. In captivity if polar bears are furnished with a 
large swimming pool, they can endure hot weather as well as the 
black bear (Hornaday). 

The brown Kodiak bear of the Kodiak Island ranges from Sitka 
to the extremity of the Alaskan peninsula. It reaches a length of 
about ten feet, and weighs nearly two thousand pounds. It is, 
however, a timid animal. It feeds on salmon and small mammals, 
but in the summer almost becomes a vegetarian.* 

The grizzly bears have high shoulders, brown hair with silvery 
gray tips and may reach a weight of about twelve hundred pounds. 
In Yellowstone Park, they have become celebrated for their excessive 
friendliness to visitors who at times are disappointed to discover 
that the animals are not as tame and harmless as dogs. (Figure 
2i6.) 

The black bear is a timid animal and an excellent climber. It is 
still to be found in the Adirondacks and the mountains of Pennsyl- 
vania and West Virginia. It feeds on berries and fish and robs 
"bee-trees." The black bear has a brown phase, brown (cinnamon) 
and black cubs sometimes being found in the same litter. 

The glacier bear., found in Alaska, the smallest species of bear in 
America, reaches a height of but two feet. Its color is bluish gray 
except for the dark brown muzzle. 

The Mustelidae are small, fur-bearing animals such as the otter, 
mink, weasel, marten, wolverine, skunk and badger. The North 
American otter is still found in the South and also in Northwest 
Canada and Alaska. It lives in a burrow usually under the roots 
of a large tree growing near the water. It reaches a length of about 

* In the spring when he emerges from hibernation the Kamschatkan brown bear 
eats sea-weed, later he grazes on herbage, and in the middle of June feeds on the migrat- 
ing salmon. In August, he eats wild peas, in September he eats berries and in later 
October, just before hibernating, he feeds luxuriously on ground-marmots. (Elton.) 



MAMMALIA 



3^S 



two feet. The sea otter is one of the most valuable of the fur-bearing 
animals. It is now raj-ely found except in Alaska. Its fur is a 
lustrous black and very thick and fine in texture. The 7nink, much 
smaller than the otter, lives along the banks of streams, but is not 




Fig. 2 1 6. Bear and cub, in Yellowstone National Park. (Photo by V. J. Mele.) 



an aquatic animal like the otter. The pine marten or " American 
sable " lives in dense forests of pine and spruce, and feeds on small 
rodents, birds and reptiles. It grows to the size of an ordinary 
house cat. Demand for their fur has reduced the number until but 
few of these shy animals remain. Pennant's 77jarten, called the 
black cat, is rather large, sometimes reaching a length of three feet 
and a weight of eighteen pounds. 

The weasel, the smallest of the marten family, is brown in sum- 
mer, but becomes the white " ermine " in winter. It kills chickens 
and small mammals, being particularly valuable in the extermination 
of rats and field mice. ^\\z ferret is a domesticated variety of the 
English " pole-cat." Formerly used in this country in hunting 
rabbits and rats, it is rarely seen today. (Figure 217, A and B.) 

The wolverine, " mountain-devil " or Carcajou, is the greatest 
thief among animals. It follows a " line " of traps, devouring the 
bait and sometimes stealing the trap. Cabins and caches are 
stripped of edibles and foodstuffs, too large to carry away, are 



386 



MAMMALIA 



dragged in the dirt. Wolverines resemble a cross between the 
badger and the bear. 

The common skunk. Mephitis mephitica, is a native of North 
America, found from Hudson's Bay to Guatemala. An allied form, 







V^ 




^.d.^ 




Fig. 217. /^, ferrets. 5, wolverine. (From L. A. Fuertes. Courtesy of Sllngerland- 

Comstock Publishing Co.) 

the conepatl, is found in South America. Preeminently an insect 
eater, the skunk destroys more beetles, grasshoppers, and grubs 
than all of the other mammals together, and also devours vast 
quantities of mice in addition. The skunk is also partial to sala- 



MAMMALIA 387 

manders, snakes and the eggs of birds nesting on or near the ground. 
Under conditions of civilization his fearlessness ^ renders him an 
important enemy of poultry. It is said that owls, eagles, and the 
puma prey upon skunks. 

The badger skunks resemble badgers in that they are expert 
diggers. They are found in South America but range northward 
into Arizona. The badger lives in burrows and feeds on ground 
squirrels and prairie dogs. It has naked soles, short legs and a 
broad, flat body. In the United States, it is found in the Rocky 
mountains and westward to the Pacific coast. (Wisconsin is called 




Fig. 218. Young red foxes. (Courtesy of A. B. Brooks.) 

the " badger " State.) In Alaska it hibernates during most of the 
winter. The European badger lives in the woods. The Asiatic 
badgers have a strong musky secretion. 

The Dog family {Canidae) have served as man's companion 
^onger than any other domesticated animal. They are found every- 
where except in New Zealand. The genus Canis includes dogs, 
wolves, foxes, and jackals. (Figure 218.) 

The common red fox is found throughout the whole northeastern 
United States extending westward to the limit of trees. Foxes 

* Few there are who will brave the overpowering scent from the anal glands of a 
skunk, which can be discharged in any direction to a distance of ten feet. The scent 
is so powerful that it can be readily detected when a mile away, and it is capable of 
anesthetizing a person. The scent is n-butyl mercaptan, C4H9SH, the excretion of 
sulphur being quite characteristic of the scent glands as well as the urine of the meat 
eaters. 



388 MAMMALIA 

feed on small mammals and upon ground birds as well as on frogs, 
lizards, insects and fruits. Foxes are extremely cunning and are 
valued by hunters on that account. A rare phase of the red fox, 
the black fox, sometimes called the " silver gray " fox, is extremely 
valuable for its fur. A single black fox skin is said to have brought 
$2,900.00. Fox farms are found in Canada and in the northern 
part of the United States. At the winter fur auction in New York 
City beginning January 23, 1928, it was reported that the silver fox 
pelts (over 800 in number) were worth more than $1,300,000. 
The majority of these skins came from a single fox farm ^ in Wis- 
consin. 

The Arctic fox has two color phases, one, brown in summer and 
white in winter; the other, gray or black in summer and blue or 
black in winter. In the far north it is snow white the year round. 
In Iceland and the Aleutian Archipelago it is dark the year round 
and is known as the " blue " fox. In Labrador the blue phase is 
rare, while in Greenland, Alaska and Spitzbergen both are common. 

The darker color makes the fox extremely conspicuous instead 
of protecting it. Roosevelt and Dugmore have both concluded 
that practically speaking there is no such thing as protective or 
concealing coloration. (See Thayer's theory, page 488.) 

The coyote or prairie wolf is a cowardly animal, stealing poultry, 
pigs, lambs and sheep, but never attacking mammals larger than 
deer. Their cry is a dog-like barking howl. They are smaller 
than the gray wolf, but somewhat resemble it. 

The red wolves have been so active of late in Texas, killing sheep, 
goats and poultry, that in the rural districts government hunters 
have been employed to kill them off. In the eight months preceding 
January, 1928, 100 of the animals were killed. Bounties as high as 
I300.00 were offered in some Texas counties. The red wolf, like 
the coyote (prairie wolf), is a solitary nocturnal despoiler. A giant 
red wolf caught recently weighed Gi^ pounds. 

The gray wolf, " lobo " or timber wolf, is a large strong animal 
ranging from Florida to Arctic America. They hunt in packs or in 
relays and destroy deer, antelope, cattle and young horses. In 
Alaska they grow to a length of over 4 feet and a height of 2^ feet, 
weighing over 100 pounds. 

^ Fromm Bros., of Hamburg, Wis., received a single check for ^1,021,071.24 in 
payment for the silver foxes sold in New York at the auction of 1928. At other auctions 
that winter, they received $267,203.00 additional. 



MAMMALIA 389 

The African and Oriental jackals are scavengers, but also rob 
hen-roosts. They feed on figs and fruits as well. 

There are over 200 breeds of domestic dogs. They are derived 
from at least seven wild species, including the jackals of Asia, the 
jackal-wolf of Northeast Africa, the gray wolf and the coyote of North 
America. 

Sub-Order Pinnipedia. {Seals and Walruses.) — The Pinnipedia 
are aquatic carnivores with their digits united by a membrane. 
The Northern fur seal iOtaria ursina) is not a true seal, but is a sea 
bear or sea lion, found on the Pribilof Islands. It spends about 
two-thirds of each year far out at sea, making a circuit of six thou- 
sand miles in the open ocean without touching land. The United 
States protects a large fur seal herd on the Pribilof Islands, Alaska. 
The California sea lion {Otariidae) feeds mostly on squids and octopi, 
but fishermen consider it injurious as a fish consumer. The true 
seals {Phocidae) have no external ears and their nostrils are dorsally 
situated. Among the common forms are the harbor seal and the 
hair seal. The bluish gray fur of the harp seal is extremely valuable. 
The hooded seal males have a nasal sac that can be inflated to a 
length of ten inches. Elephant seals (twenty feet long) are nearly 
extinct, but a few were discovered recently at Guadaloupe Island. 
Walruses {Odobenidae) are clumsy on land, but have extremely 
powerful tusks (canine teeth) and can wreck small boats. They 
eat shellfish, crustaceans and aquatic plants. Formerly supplying 
the Alaskan natives with fuel, light, harness and boats, the demand 
for walrus oil has led to their almost complete extermination. 

Fossil Relatives of the Carnivora. — Primitive Creodonta are 
found in the Eocene of North America, Europe, and Africa, and are 
almost indistinguishable from the Insectivora and Ungulata of that 
period. Fossil dogs appeared in the Eocene of North America. 
Fossil cats are known from the Oligocene period where the huge 
saber-tooth tigers lived from the Miocene to the Pleistocene. Bears 
came in with the Miocene, and the great cave-bear ( Ursus speleus) 
of Europe was hunted for food during the Pleistocene period. Seals 
and walruses have descended from primitive Pinnipedia of the 
Miocene period. 

Order VI. Rodentia. — Vegetable-feeding, mostly of small 
size, with furry integument, clawed digits, and usually plantigrade 
limbs. Clavicle usually present. No canines, never more than two 
incisors in lower jaw and but two in the upper except in the Lepo- 



390 MAMMALIA 

ridae, all elongated, chisel-like, growing from persistent pulps; 
premolars few. Placenta deciduate and disc-shaped. Cecum 
large. (Figure 219.) 

Rodents vary in size from the porcupine of three feet in length 
to the small mouse about three inches long. Squirrels {Sciuridae) 
are found everywhere except in Australia and Madagascar. Four 
species are found in the United States and Canada. 

The Calijornia ground squirrel {Citellus beecheyi) (see Figure 
220) lives in and on the ground, storing its food of fruits, nuts, and 
grain in the ear in its underground burrows. It is of particular 
interest since it carries bubonic plague caught from rats. 

Other squirrels include the Eastern Gray squirrel which lives in 
the tree tops and the 7'ock squirrels or " chipmunks " which live in 
fences and among the roots of large trees. The largest squirrel in 
the world is the great Malabar squirrel of India, which grows to be 
eighteen inches long, with a tail fourteen and one-half inches long. 

The Easter?i chipjnunk (Tamias st?-iatus) ranges from Illinois 
eastward. It is a lively little creature about ten inches long, and 
seems fond of nests in rocky crevices and decayed tree trunks. It 
usually has several entrances to its tunnel. It feeds on acorns, 
nuts, and grains but is also a consumer of mice, birds' eggs and 
insects. Its chief enemy is the weasel but it is also preyed upon by 
birds. 

The flying squirrels {Sciuropterus) are not able to fly, but by 
means of a furry membrane spread from the anterior to the posterior 
limbs they plane from one tree or branch to another. The Asiatic 
flying squirrel reaches a length of eighteen inches. 

The p}'airie-dogs (Cynomys) live in villages on the plains. They 
are a great pest in the cattle country. Rattlesnakes visit their 
burrows in search of young " dogs " and burrowing owls are fre- 
quently found in vacated burrows, but the " happy family " does 
not exist. 

The woodchuck, or "groundhog," lives on clover and other grasses 
and may enter isolated gardens. He lives in a burrow and hiber- 
nates in November. It is traditional that he wakens on " ground- 
hog day," February 2, and " if he sees his shadow, sleeps six weeks 
longer, which means a cold spring," 

The gray marmot is found in the Northwestern part of North 
America and is called the " whistler " on account of its danger signal. 



MAMMALIA 



39^ 




Fig. 219. Red squirrel. (Courtesy of Canadian National Railways.) 




Fig. 220. California ground squirrel {Citellus beecheyi). (Courtesy of Joseph Dixon, 

University of California.) 



392 



MAMMALIA 



The Alpine marmot is. a similar form, hibernating a dozen in a group, 
packed into a hair-lined burrow. 

The North American beaver {Family Castoridae), an aquatic 
rodent, has a heavy body, webbed hind feet, and a large flat tail. 
Contrary to the statements of some nature fakers, the tail is not 







ii^'^ 











Fig. 221. y^, chipmunk. 5, flying squirrel. C, prairie dog. D, beaver. 
L. A. Fuertes. Courtesy of Slingerland-Comstock Publishing Co.) 



(From 



used as a trowel or a sledge, but as a danger signal and in swimming 
and diving. The beavers fell trees up to eighteen inches in diameter 
and quickly dam streams to flood the entrance to their burrows. 

The largest family of rodents and the most important economi- 
cally is the family Muridae to which belong the rats and the mice. 



MAMMALIA 



393 



The genus Rattus includes a number of species, all of which are 
important as disease carriers. (Figure 222.) 

The brown rats (R. norvegicus) destroy grains, poultry and nesting 
birds, carry away eggs, sometimes cause fires, and even bite through 
lead pipes and cause floods. The black rat of England was the 
carrier of the " great plague " 
of 1665 which destroyed one 
hundred thousand people. 
Brown rats eventually drove 
the black rat out of England. 
It is now chiefly confined to 
ships. It disseminates bu- 
bonic plague, which is trans- 
mitted by rat -fleas to ground 
squirrels. Ships in port have 
three-foot metal discs guard- 
ing their hawsers. Poison 
baits and fumigants are used 
to destroy rats in ships and 
storehouses that are not rat- 
proofed. 

The Eastern wood rat 
(pack rat, trade rat), the 
most handsome of the rats, is 
noted for its mental capacity. 
It stores food, but also steals 
tools, silverware and even 
watches, and stores them 
away. Vernon Bailey states 
that they are edible, " better 
than Gray Squirrels." 

The albino rat is our most 
important mammal for ex- 
perimental purposes, and has 
been inbred for nutrition and 
other studies (see p. 441). 

The common house mouse 
{Mus musculus), a species introduced from Europe, is an important 
enemy of food stuffs and especially injurious in warehouses. The 
field mouse or meadow mouse (see Figure 223) is a short-eared, 




Fig. 222. Brown rat infested by Cysti- 
cercus fasciolaris. (A. T. Hopwood, Para- 
sitology, vol. 14, no. I.) 



394 



MAMMALIA 




short-tailed animal with a thick body. It feeds on roots and 
grasses and also turns its attention to young fruit trees, shocks of 
corn, and fields of alfalfa. The pine mouse is a burrowing mam- 
mal feeding largely underground. It is of great injury in truck 

gardens and has damaged many 
small trees. 

Lemmings, short-tailed prai- 
rie-dog-like forms, have a max- 
imal production which was in 
times past every four years, but 
now comes about every ten 
years. Their migrations (see p. 
418) are a sign of over-produc- 

TI" T. ~, 'Z. ' tion. It is interesting to note 

223. Meadow mouse. (Courtesy ° 

of W. Va. Exp. Station.) that in their enemies, hares, 

Arctic foxes, weasels and lynxes, 
there is a corresponding cycle of increase. 

The musk-rat or musquash is a small aquatic rat-like rodent 
with a broad blunt head, thick-set body and short legs. Its long 
tail is almost naked. Musk-rats are widely distributed through the 
United States. They are omnivorous, feeding on the stalks and 
roots of flags and reeds, and on animals such as insects, fish and shell 
fish. Musk-rat skins are dyed and sold as " Hudson Seal " or 
" electric Seal." The dormouse, a small form found in the Old 
World, resembles a small squirrel. It spends about six months of 
the year " wrapped in a profound sleep." It utters a shrill whistling 
snore surprising in its volume. The American porcupines are 
arboreal forms. They are well protected by spines which readily 
pull out and being barbed remain in the flesh of the enemy. Jerboas 
or jumping-mice {Dipodidae) (Figure 224 A) have kangaroo-like 
tails and hind legs and are reputed to jump ten feet, 

TYiQ pouched gophers {Geomyidae) (Figure 224 B) are burrowing 
rodents found in Central America and the central plains of North 
America. The red pocket gopher is a vicious, thieving animal, 
tremendously injurious to fruit trees, grain and vegetables. It also 
honeycombs and weakens the banks of canals and irrigating ditches 
m the Mississippi valley. Farmers use traps and strychnin poisoned 
grain in an attempt to kill ofi^ the pests. 

The hare and rabbit family {Leporidae) includes two quite distinct 
groups. The rabbit group {Sylivilagus) is represented in the United 



MAMMALIA 



39S 



States by the gray 7'abbit or " cottontail " which is found from New 
England to Yucatan. Although cottontails are small with relatively 




Fig. 224//. Egyptian jerboa. (Courtesy of N. Y. Zool. Soc.) 




Fig. 2245. Pocket gopher {Thomomys a'xahnee). (Courtesy of T. I. Storer, Univ. oi 

Cilif.) 



short, weak limbs, they are exceedingly cunning and burrow in cities 
and towns, rearing families in apparently quite accessible places. In 
the West, cottontail rabbits are such pests that rabbit-proof fences. 



396 MAMMALIA 

poison baits, trapping and hunting are all resorted to, in an attempt 
to decimate them. 

The hare family {Lepus) includes the Jack hare (sometimes called 
the Jack rabbit), the prairie hare, the vaj-ying hare and the polar hare. 
The " Jack hare " can distance a speedy greyhound and some hunters 
insist that it can beat a rifle bullet! The hare is a large, long-legged, 
long-eared animal which does not burrow, but rears its young in a 
nest. 

Hares and rabbits girdle trees and eat garden vegetables, clover 
and alfalfa. It is said that except when famished hares exhibit 
considerable delicacy of taste, selecting only certain varieties of 
soy-beans and alfalfa. Rabbits, introduced into Australia and New 
Zealand, spread rapidly and destroyed the grass so that sheep died 
of starvation. 

Tularemia, a disease somewhat similar to spotted fever,^ is car- 
ried by lice and ticks from one rabbit to another. It may cause 
serious epidemics and reduce the number of rabbits and ground 
squirrels considerably. Man is susceptible to tularemia. It is 
transmitted from the bites of ticks or lice, or from handling diseased 
rodents. 

Fossil Relatives of the Rodentia. — Rabbits and squirrels were 
first found in the Oligocene of North America, while the beaver, rats, 
and mice appeared in the Pliocene of Europe. 

Order VII. Edentata. — Clawed, without enamel on the teeth; 
teeth absent from the anterior part of the jaw. Great number of 
sacral vertebrae, as many as thirteen in some armadillos. Brain 
sometimes low, sometimes of comparatively high organization. 

There are three genera of South American ant-eaters {Myrineco- 
phagidae), all lacking teeth, but with extremely long protrusible 
tongue, plentifully coated with a thick secretion developed from their 
salivary glands. They have long snouts and powerful bodies 
adapted to tearing bark from trees or ripping open ant hills. (Figure 
225.) 

The great ant-eater may reach a body length of five feet with a 
tail as much as two feet long. It is able to defend itself against dogs 
and snakes. The single oflfspring rides on the back of the mother, 
remaining with her a year. The tamandua, a small ant-eater found 

^ R. R. Parker and J. S. Dade, Tularaemia in Sheep in Nature, Pub. H. Reports, 
vol. 44, Jan. 18, 19-9, found Bacterium tularense in the flesh of sheep. Probably the 
wood tick, Dermacentor andersoni, transmits the disease from jack rabbits to sheep. 



MAMMALIA 



397 



as very 



in South America, reaches a length of about two feet. It h 
large front claws. 

The sloths {Bradypodidae), found only in the New World, are 
arboreal forms, never descending to the ground if possible. They 
are nocturnal feeders and their hair usually contains quantities of 
green algae, causing them to resemble branches. The three-toed 
sloth has nine cervical vertebrae, while the two-toed sloth has six 
instead of the seven usually found in mammals. 




/i 



>-»^: ' • '■■■ ;■.'*- 



^ 



Fig. 225. Giant ant eater. (Courtesy of N. Y. Zool. Sec.) 



The three-banded armadillo {Dasypodidae) of Argentina is able 
to close itself into a tight round ball so that it resembles a nut. 
The nine-banded armadillo is somewhat larger and is found ranging 
from Texas to the central part of South America. It has been 
studied recently at the University of Texas, since it offers a most 
interesting example of quadruplets, identical of course. Armadillos 
eat insects and worms, and occasionally salamanders and lizards. 

Fossil Relatives of the Edentata. — Fossil remains of the modern 
sloths and ant-eaters are unknown, but the extinct ground sloths 
{Megatheriidae) with the head and teeth of a sloth and the tail of an 
ant-eater were found in the Pleistocene, one species having reached 
the length of nearly twenty feet. A large armadillo-like form known 
as Glyptodon was found in the Pliocene of the Americas. 

Order VIII. Ungulata. — Terrestrial, usually herbivorous, nearly 



398 



MAMMALIA 



always hoofed. Clavicle absent, canines small or absent, premolars 
and molars well developed with broad crowns. 

Sub-Order Hyracoidea. — The hyrax ( Hyracoidea), a small animal 
found in Africa, is probably the form described in the Bible as 
" Cony." It has about twenty-two vertebrae that bear ribs. It has 
in addition to a cecum a ^poAVob-ectal cecae. Superficially it resembles 
the rabbit, having a hare lip and an extremely short tail. Its front 
feet have four toes, while the hind feet have three. (Figure 226.) 




Fig. 226. Hyrax. (Courtesy of N. Y. Zool. Soc.) 

Sub-Order Proboscidea. — The elephants have no clavicle. They 
have an extremely thick skin, huge five-toed legs and a long nasal 
proboscis. The incisors of the upper jaw grow to form tusks. 
Elephas indicus has been used as a beast of burden in India for many 
years.'^^ It reaches a height of less than ten feet. It is more intelli- 
gent and docile as well as more powerful than the African species. 
Elephas ajricanus has a shorter, more rounded head than the Asiatic 
and its ears are enormous, covering the back of the head and the 
neck. Both the male and the female have tusks (elongated incisor 

^»Livy in describing Hannibal's passage over the Alps (Livy, Book 21. Chapter 
28) discusses the manner in which historians supposed that his war-elephants were 
transferred across the Rhone River. Some reported that the elephants were induced to 
swim, while others described the manner in which they were ferried on long rafts. 



MAMMALIA 



399 




Indian 



African 



Fig. 227. A, Indian rhinoceros. B, South American tapir. C, elephants. (From 
L. A. Fuertes. Courtesy of Sllngerland-Comstock Publishing Co.) 



400 MAMMALIA 

teeth) while the African form has three toes on its hind feet instead 
of four. It reaches a height of twelve feet. (Figure 227.) 

Sub-Order Perissodactyla. — Perissodactyla are o^^-/o^(^Ungulata 
with an uneven number of digits; the axis of symmetry passes 
through digit three. Premolars and molars are completely folded. 
Stomach simple; cecum large. Gall bladder absent, teats situated 
in the groin and placenta diffuse. (Horse, tapir and rhinoceros.) 

The tapijs {Tapiridae), found in tropical America and India, are 
as old a family as the horses {Equidae). They have four-toed fore 
feet and three-toed hind feet. The nose and upper lip are elongated 
into a proboscis. Tapirs are enemies of the cocoa plant. They are 
hunted for food and for their hides. 

The rhinoceroses have extremely thick skin deposited in folds 
resembling plates of armor. The East Indian species has one nose 
horn, and the African white rhinoceros has two. Nose horns, out- 
growths of skin like whalebone, grow at the base as the tip wears 
away. They are used as weapons, and powdered for medicines. 
The rhinoceros injures cane and melon fields, and cacao plantations. 

The horse {Equidae) has a geological record back to the Eocene 
Epoch when the little Eohippus had four complete toes and the 
splint of a fifth on its fore feet, while the hind feet had three com- 
plete toes and a splint of the fifth. It was about the size of a small 
dog. (See p. 526, The Evolution of the Horse.) 

All our horses have been introduced from the Old World. Wild 
horses are found at the present time in Asia {Equus heinmonus, the 
Asiatic Wild Ass; and Equus przewals kit, Przewalsky's Horse) and in 
Africa (£. asinus, the African Wild Ass; and the Zebras, Equus 
zebra, burchelli, and Quagga). 

The African Wild Ass has been domesticated and is utilized as 
our donkey. The White Ass was used in Africa as a means of 
transportation for the great, centuries ago. Andrews states that the 
Asiatic Wild Ass is capable of bursts of speed of 60 miles an hour. 

Hybrids. — The " mule," a hybrid between the horse and the ass, 

is an extremely powerful draft animal. Male hybrids are as a rule 

infertile,^ and only a few cases of fertile hinnies ^ have been reported. 

8 Wodsedalek, J. E. 1916. Causes of sterility in the mule. Biol. Bull., vol. 30, 

PP- 1-39. 1916. 

8 Groth, of the Texas A. and M. College, has reported a case of "Old Beck," a 
fertile mule, who in 1920 produced a daughter, sired by a Jack, and later produced a son 
sired by a stallion. It is further reported that the horse-like colt has sired a healthy 
colt, making "Old Beck" a grandmother. 



MAMMALIA 401 

The United States Department of Agriculture has experimented 
with the zebra and the quagga, hybridized with the horse, but has 
been unable to secure any notable improvement over the mule. 
The African quagga is now extinct. 

Artiodactyla. — Artiodactyla are even-toed ungulates in which the 
third and fourth digits form a symmetrical pair. Premolars are 
smaller than molars; stomach usually complex, cecum small. 
Placenta diffuse or cotyledonary. 

The Artiodactyla are divided into the Ruminants and the Non- 
Ruminants. The Ruminants are that extremely important group 
of domestic animals which have been of service to man for thousands 
of years — cattle, sheep, goats, and camels; also such non-domesti- 
cated types as antelopes, deer and giraffes. The Non-Ruminants 
include pigs, peccaries and the hippopotamus. 

The African hippopotamus or " river horse " once ranged over 
Europe and India. It is thick skinned and almost devoid of hair. 
Its perspiration is reddish. The hogs {Suidae) are important sources 
of food supply. The United States produces over one-third of the 
hogs of the world, and exports many. The wild boar has been hunted 
for centuries by the sportsmen of Europe. Its tusks are elongated 
canine teeth. The African wart hog has such a horrible appearance 
that it is said to be the ugliest of mammals. Another African form, 
the " red river hog" is one of the most beautiful of the Suidae, having 
long slender ears and a glossy coat. The collared peccary ox javelin 
(hunted on horseback in Mexico) and the white-lipped peccary range 
from Mexico into South America, frequenting the upland jungles. 

The ruminants are animals that have four parts to their stomachs 
and regurgitate the food from the rumen or paunch, chewing it as 
the " cud." (See Figure 241, page 434.) 

The Chevrotains of India and Africa are hornless forms, resem- 
bling both the deer and the pig. They have in some cases four toes 
reaching the ground, do not chew the cud, and have simple stomachs 
with only three chambers. The " deerlets " have changed but little 
since the Miocene period. 

The Camelidae are able to retain twenty quarts of water in the 
tightly closed water cells of the rumen of their stomachs, and march 
for a week over the sanded wastes. Their nostrils are guarded by 
valves, their tough cartilaginous mouth permits them to eat thorny 
vegetation, and they walk over the sand on padded feet. The hujnp 
of the camel is a reservoir of nutriment to the animal and a satis- 



402 



MAMMALIA 



factory human food. The one-humped Arabian camel Is very speedy. 
The two-humped Bactnan is short legged, and long haired. It is 
especially important in the heat and cold encountered in Mongolia. 
Camels were introduced to the United States in 1850 at the Gold 
Rush and later purchased for use in the Union Army. The llama 
is a Peruvian beast of burden. In Peru, Chile, and South Africa, 




Moose 



Fig. 228. A, Virginia deer. 5, moose. C, elk. (From L. A. Fuertes. Courtesy of 

Slingerland-Comstock Publishing Co.) 



the alpaca {el paco)^ a somewhat smaller form, is bred for its valuable 
long hair. 

The deer family ( Cervidae) are differentiated from the other 
ruminants by the presence of bony antlers. The male deer of most 
species have solid horns which are shed once a year, close to the 
skull, and are fully renewed by rapidly growing out in a soft state 



MAMMALIA 



403 



called the velvet (Hornaday). The first pair of antlers grown during 
the second year are two straight, slender spikes (" dag antlers "). 
The fully grown antlers branch several times. The American Elk 
or Wapiti {Cervus canadensis), tall as a horse, with a beautiful mane 
and a pair of large antlers, is termed by Hornaday " The king of the 
Cervidae." The elk browses and grazes. The European red deer 
are related to the elk. 




Fig. 229. Mule deer in "velvet." (Photo courtesy of Canadian National Railways.) 

The mule deer or Rocky Mountain " black-tail," (Figure 229) the 
largest of the North American " deer," ranges as far east as western 
Dakota, preferring a dry climate and a high altitude. It is difficult 
to keep in a park. The Virginia deer or " white-tail " deer is a 
forest animal noted for its tendency to hunt cover. Its antlers 
project forward. 

The American caribou is a deer-like animal ranging farther north 
than any other hoofed animal except the musk ox. The woodland 
caribou shifts away the snow with its flanged horn and feeds on 
grasses, moss and lichen. Other caribous include the Newfoundland 



404 MAMMALIA 

caribou and the barren ground caribou. The domesticated reindeer 
in this country were imported from Siberia and Lapland to Alaska. 
In the reindeer, horns are present in both sexes. Caribou and 
reindeer are readily interbred. The American moose {Alces ameri- 
canus) is the largest animal of the deer family, not excluding the 
celebrated " Irish elk." It stands over six feet high at the shoulder, 
its legs are four feet long and its heavy antlers spread over six feet 
in width. The male has a long strip of skin, the " bell," hanging 
down from its neck. The female lacks bell and antlers. The musk 
deer lacks horns and has musk glands highly developed in the male, 
which furnish the basis of many perfumes. 

The giraffes {Giraffidae) of Africa, although somewhat like the 
deer, have no antlers but short horns covered with hairy skin. The 
giraffe, in spite of its tremendously long neck, has only seven cervical 
vertebrae. It reaches a height of twenty feet from its front hoofs 
to the top of its head. Its eyes are large and its face mild appearing, 
although it is adept at kicking in all directions. 

The long neck of the giraffe has, according to the Lamarckian 
theory, developed as a result of the efforts of the animals to reach 
the elevated branches of tall trees. (See p. 514-) 

It is believed that the parent stock, the three-horned giraffe 
{Giraffe camelopardalis) ^ has given off the other species such as the 
two-horned giraffe of Southern Africa and the six-horned giraffe of 
Western Uganda. Giraffes are silent, even the female making no 
noise whatsoever. 

The North American prong-horn {Antilocapra atnericana) has 
horns which in the male are branched like those in the deer. The 
horns of the female are unbranched. W. L. Finley reports that the 
pursued prong-horn antelope runs at a speed of about forty-five 
miles an hour. 

The cattle family (Bovidae) include the wi/d catt/e, sheep, goats, 
the bison, and the antelopes. There are many breeds of domestic 
sheep which are used for flesh and for wool. Persian and Astrakan 
lambskins are valued in fur trade.^'' The/at-tail sheep of Asia have 
a tail that weighs as much as fifty pounds. The Spanish Merino 
sheep introduced into Australia, Africa and United States is valued 
for its fine long wool. There are six North American species of wild 

^^ Tight curled fur from a lamb 3 days old is called " broadtail." The same lamb 
at 6 to 10 days of age would give "Persian Lamb Fur." At three weeks the fur would 
be sold as Karakul. 



MAMMALIA 



405 



sheep. Both male and female in Dorset sheep are horned, while the 
Suffolk breed are both hornless. 

The Rocky Mountain Bighorn (Figure 230) is a large strong an - 
mal adapted to its life on the mountain top. It is valued for its 
massive horns and its flesh. The Chamois of the European Alps, 
like the Rocky Mountain goat, is termed a goat antelope. The 




Fig. 230. Rocky mountain sheep. (Photo courtesy of Canadian National Railways.) 

Rocky Mountain goat is not a true goat, but is our only native goat- 
like species. It has very high shoulders, thick legs and a long face. 
It lives just above the timber line on high mountains and has ex- 
ceedingly sharp hoofs adapted to ice and snow. 

The true goats include the Spanish Ibex, the Steinbock of the 
Tyrolean Alps and the Persian Wild goat. The goats of Cashmere 
and Thibet furnish extremely fine wool, while the Angora goat (Asia 
Minor) also furnishes a highly valuable silky hair. In Southern 
Europe, herds of goats are driven from house to house and milked 
at the customer's door. 

The ibex is a large wild goat with horns that extend nearly 
straight up in a scimitar-like curve. Formerly found in the Alps, 
they are now limited to the Himalaya Mountains, Syria and Abys- 



4o6 



MAMMALIA 



sinia. The Himalayan ibex stands forty inches in height and has 
horns that reach a length of fifty inches Another Himalayan goat, 
the markhor^ has enormous black twisted horns, five feet in length, 
and a yellowish mane over one foot long. It is supposed to be the 
ancestor of the Angora goat. 

The antelopes^ also Bovidae^ include the koodoos, elands, spring- 
bucks, gazelles, hartebeasts, gemsbucks, water bucks and black 
bucks found in Africa. Space does not permit a description of these 
forms. 




Fig. 231. Asiatic ibex. (Courtesy of the Field Museum of Natural History.) 



The musk-ox^ found in the frozen north, has a remarkable ability 
to subsist on grasses and willows, covered by Arctic snows. The 
males have a strong musky odor. 

The wild ox of Europe ( Bos primigenius) is one of the ancestors 
of our cattle. From this primitive species it is supposed that most 
of the English, North German, and Holland cattle have descended. 
(See p. 494, Domestication of Mammals. )^°" 

The Wisenty or European bison {Bos bonasus), somewhat re- 

^""It is related that bullfighting was introduced into Spain from Rome. The 
Romans, feeling that it was too brutal a sport to force animals to fight for their amuse- 
ment, chose the lesser evil and used gladiators. 



MAMMALIA 407 

sembles our American bison or buffalo, but is considerably taller. 
It is a forest lover. Belated efforts have saved a few wisents in the 
Caucasus Mts. The American bison, or " buffalo,'' is not a true 
buffalo since it has a hump. It was first seen by white men in 
Anahuac, the Aztec capital of Mexico, in 1521. The "buffalo" 
once roamed over the plains of the West and migrated from North 
to South, thirty-six hundred miles, extending up the Western slope 
to the Canadian home of the musk-ox. From East to West it 
ranged about two thousand miles. The American Bison Society 
has prevented the complete extinction of the buffalo and there are 
now a number of flourishing herds. 

Yaks are used in Thibet as beasts of burden, while their milk and 
flesh are excellent food. Their skins furnish clothing, harness and 
tent covers and their hair is twisted into ropes. Their dung is the 
only fuel available to the Thibetans, when snow hems them in. 

The Indian zebu has a fleshy hump above the shoulders, a devel- 
opment of loose skin on the underside of the neck, a short, steep rump 
and quite long legs. Different breeds are found in Asia and Africa. 
" Brahman " cattle were introduced into the United States in 
considerable numbers in 1906, when A. P. Borden imported fifty-one 
head from India to Texas. In Texas, as well as in Brazil, pure bred 
zebus and hybrids are valued highly since both are free from ticks 
and cattle-fever, and remarkably resistant to drouth and heat. 

Certain cattle called Podolian are found in Southwestern Russia 
(Podolsk) and in Hungary and are said to be descended from the 
Giant Ox, Bos taurus primigenius. Mature cows reach a height of 
nearly five feet and a weight of twelve hundred pounds, while bulls 
are even taller and weigh eighteen hundred pounds. Podolian 
cattle are not valued for milk production, but as draft animals. 
They are quite resistant to disease. 

The True Buffaloes. — The Cape buffalo ( Bos caffer) has thirteen 
pairs of ribs like the ox family. The hair of the back is directed 
backwards. The African buffalo lives in reedy swamps. Explorers 
fear the water-buffalo more than all other African game. The 
Asiatic buffalo has the hair directed forwards on the anterior portion 
of the back. The Indian buffalo is of large size with widely separated 
horns. It is stronger than the tiger and able to combat the ele- 
phant. All buffaloes are fond of water and cover themselves with 
mud to keep off the gad-flies. 



4o8 



MAMMALIA 



Cattle Hybrids.— One of the oldest of the cattle hybrids has been 
that with the I^ison, or " buffalo." (Figure 232.) Potent " cattalo " 
males are rarely produced and there is a relatively low percentage of 
fertility among the hybrid cows. In the Dominion of Canada, Gal- 
way cattle have been successfully hybridized with yaks in an attempt 
to produce a stock even more cold-resistant than the hardy Irish 
breed. Zebu-cattle hybrids, developed in Louisiana, Texas, and 
South America, are important additions to the breeds of beef cattle 
since they are disease resistant. The hybrid male is not fertile. 




Fig. 232. Cattalo at Wainwright, Canada. (Photo courtesy of Canadian National 

Railways.) 



Fossil Relatives of the Ungulata. — In the lowest Eocene the fossil 
ancestors of the clawed mammals (Unguiculata) are very much like 
those with hoofs (Ungulata). Both are five-toed, flat-footed forms 
with freely movable fore limbs. One of the most primitive forms 
which occurred in the lower Eocene (Phenacodus) reached the size 
of a large sheep. In North America the mastodon {Mammut 
americanum) appeared in the Pleistocene. The mammoth {Elephas 
primigenius), a form whose height was usually less than nine feet, 
appears in the Arctic ice of Northern Siberia. The Imperial ele- 
phant (£. imperator) reached a height of over thirteen feet. The 



MAMMALIA 409 

horse family arose in the Lower Eocene of North America, and 
Eura'sia. Its descent has been traced from a primitive five-toed 
Ungulate. True pigs (Sus) are known from the Middle Eocene. 

The giraffes, found from the Pliocene to the present, were not 
confined to Africa, but were present in Eurasia as well. The llamas 
and camels were found on the North American continent in the 
Upper Eocene. Later they migrated into South America, Asia, and 
Africa. 

Order IX. Sirenia. — Aquatic with moderate-sized head, 
depressed fish-like body, paddle-like pectoral limbs, pelvic limbs 
absent, horizontal tail fin. No dorsal fin. Integument thick, 
wrinkled and hairless. Snout inconspicuous, nostril openings 
paired and dorsal; cervical vertebrae unfused, clavicle absent. 
Fore legs pentadactyle, often with rudimentary nails; always a 
flexible elbow. Brain comparatively small, convolutions ?wt highly 
developed. Testes abdominal; teats are two in number and pectoral 
in position. Uterus two-horned and the placenta non-deciduate 
and zonary. 

The dugong is the only Old World Sirenian. It reaches a length 
of fourteen feet, and was once so abundant off the coast of Queens- 
land that a dugong fishery was established at Moreton Bay (Horna- 
day). 

The manatee or sea cow reaches a length of twelve or thirteen 
feet and a weight of twelve hundred pounds, superficially resembling 
a seal. Its tail, a rounded disc, is a powerful propeller. The 
Florida manatee reaches a length of about nine feet. Nearly ex- 
terminated, a fine of $500 protected it till it is now on the increase. 
The flesh of the Sirenia is considered a delicacy by some. Monks in 
South America eat all aquatic mammals on fast days, as they con- 
sider them fish. 

Stellers sea cow {Rhytina), the " Arctic sea cow" furnished food 
for Captain Bering when his ship was wrecked on Bering Island in 
1741. Steller, the naturalist of the Bering expedition, reported 
their length as about twenty-five feet and weight as much as eight 
thousand pounds. The species was exterminated in 1854. 

Fossil Relatives of the Sirenia. — The sea cows originated in the 
Eocene of Egypt, and the West Indies, and were later found in 
Europe and America. It is supposed that the sea cows and the 
elephants may have been derived from a form occurring in the 
Middle Eocene. 



4IO MAMMALIA 

Order X. Cetacea. — Aquatic with large head, fish-hke body, 
thick hairless skin, pectoral limbs paddle-like, pelvic limbs absent, 
horizontal caudal fin. So that animals may breathe while feeding, 
the larynx is prolonged into a tube extending through the pharynx 
to the choanae, from which the nostrils lead directly upwards to the 
single or paired external opening. Sole organ of respiration, nose. 
Eyes small, external ears lacking, mammae close to sexual opening. 
Teeth either present in large numbers, similar and conical; or out- 
lined early, then resorbed and replaced by large horny plates of 
baleen (whalebone). 

Baleen whales are toothless, but have plates or strainers of 
whalebone suspended from the upper jaw. The largest of the 
baleen whales is the great sulphur-bottomed whale which may reach 
a length of over one hundred feet. The " right whales^' also whale- 
bone whales, produce excellent oil. The sperm whales have a narrow 
beak-like lower jaw with heavy conical teeth arranged in a double 
row. They reach a length of eighty feet and could have swallowed 
Jonah. Ambergj'is^ used by druggists and perfumers, is formed in 
the intestine of the sperm whale apparently as concretions around 
the beaks of cuttlefish. It is worth about ten dollars per ounce. 
(Figure 123-) Of the 27,566 whales caught in the season 1 928-1 929, 
there were 13,650 blue whales. Nearly two million barrels of oil 
were yielded. Whale meat is now used extensively for food in 
Japan, but Norway leads all countries in whaling and caught nearly 
15,000 in 1928-1929. 

The dolphin has a slender, cigar-shaped body, a small head and a 
long narrow beak. It reaches a length of seven and one-half feet. 
Teeth are present on both its jaws. The short-beaked dolphin found 
in the Pacific Ocean is the most attractive in appearance. The 
porpoise is jet black with a blunt head. It does not reach a length 
greater than four and one-half feet, and rarely leaps from the water. 
It feeds on herring and menhaden. (Figure 233.) 

The narwhal {Monodon monoderos^ reaches a length of sixteen 
feet and the male has a long ivory canine tusk twisted from left to 
right and extending from six to eight feet. The killer " whale " 
{Orca) reaches a length of twenty feet and has a back fin from four 
to six feet in height. It kills whales, seals and sea lions, using its 
teeth as large as those of the largest whale. Hornaday mentions 
one killer " whale " that captured and swallowed alive four small 
porpoises. Another observer reported that a single Orca ate 



MAMMALIA 



411 



twenty-four seals off the Pribilof Islands. The black fish reaches 
a length of about eighteen feet and has been taken in great quantities 
on account of its valuable jaw oil. It is able to elevate itself ver- 
tically in the water, standing on its tail. The white " whale " 
is found in the far North, where it is said to ascend the Yukon River, 
Alaska, for seven hundred miles. 




Fig. 233. Side view of porpoise at Woods Hole, Mass. (Photo by Julian Scott.) 



Fossil Relatives of the Cetacea. — Certain primitive Eocene 
whales seem transitional from early Carnivora. The toothed whales 
are found in the Middle Tertiary, and the sperm whales appeared 
in the Upper Eocene. Whale-bone whales are known from the 
Miocene to the present. 

Order Primates. (Lemuroidea, Anthropoidea, Hominidae.) — 
The Primates include the Old and New World monkeys and the 
most highly developed Primate — man. For the most part the 
Primates inhabit a warm climate. Chiefly arboreal in habits, we 
find that with the exception of man, they feed on fruit, insects and 
birds, and do not engage in the chase after terrestrial prey. 

Characteristics. — Primates have from 32 to 36 teeth, a closed 
orbit, and two pectoral mammae. They excel in the development of 
the nervous system, having large richly convoluted cerebral hemi- 
spheres, but are comparatively primitive when bones, muscles, 
teeth, and other organs are taken into account. Nearly all are 
adapted to an arboreal life; the limbs are prehensile owing to the 
pollex and hallux being more or less completely opposable to the 
other digits. There are nearly always five nailed digits. Clavicles 
are well developed. They have no foramen above the inner condyle 
of the humerus and the femur rarely has a third trochanter. The 



412 MAMMALIA 

stomach is generally simple. The placenta may be non-deciduate, 
or deciduate and metadiscoidal. 

Lemurs {Le?nuroided), the lowest division of the Primates, in- 
clude the tarsier, the aye-aye and the lemurs. They have long, 
fox-like muzzles, small ears and 32-36 teeth. In the center of the 
upper jaw there is always a toothless gap. The ruffed , or black and 
white lemur, the largest of the race, is about the size of a house cat, 
has a very long tail, and beautifully soft black and white fur. Other 
lemurs, the mouse lemur ^ the dwarf lemur and \\^^ fat-tail lemur ^ are 
much less beautiful than the black and white lemur. They aestivate 
during the hot dry seasons, living on stored-up fat. The " slow " 
lemurs, found in West Africa and East India, are extremely sluggish, 
live in trees and eat fruits, insects, birds' eggs and young birds. 
The aye-aye of Madagascar resembles a large big-eyed squirrel with 
the face of a weasel. It has but 18 teeth, with large incisors and 
no canines. Its third finger is extremely slender and elongated and 
is used in securing food and in making the animal's toilet. The 
female constructs a nest for her single offspring. The tarsier is 
found in the forests of Borneo and the Philippine Islands. It is 
about the size of a small rat, has a long tufted tail and hind legs 
considerably longer than the front ones. Its paws have long bony 
digits with pads enabling it to climb smooth bamboo trees. It is 
nocturnal, hunting for insects and lizards. 

Monkeys. — The Platyrrhina (broad nosed), or American mon- 
keys, have a wide space between the nostril openings which are 
directed outward. The larger species have prehensile tails. 

The marmosets {Hapalidae) are the lowest in the scale of the 
American monkeys. They are small, delicate creatures with hair- 
less faces, large eyes and very long tails. The hair is abundant and 
silky, standing up on the head in a ruff. Their tails are not pre- 
hensile. The Saki monkeys are black shaggy-haired animals with 
a long black chin beard and a large hairy, non-prehensile tail. 
They come from tropical South American east of the Andes and are 
of medium size. The owl monkeys, also from South America, have 
long, hairy non-prehensile tails and extremely large, owl-like eyes. 
The squirrel monkeys are extremely active and nervous and must be 
kept in cages. They are arboreal, preferring insects as their food. 
The Cebidae, found in South America, have 2^^ teeth, flat nails and 
frequently have a prehensile tail. The capuchin, or " ring-tail " 
monkey {Cebus), comes from Central and South America. It has a 



MAMMALIA 413 

white throat and forehead with a brownish or black body. It is 
frequently seen in captivity. There are six species of howling 
monkeys {Mycetes). They have a large sound-box, developed from 
the hyoid bone, and their concerts may be heard more than a mile. 
The spider tnonkeys {Ateles) have long slender legs and tails and 
small, round heads. Their long, prehensile tails are used to swing 
by and with limbs outstretched they do somewhat resemble a 
spider. They are found as far North as Mexico. They are fre- 
quently carried by organ grinders. 

The Old World monkeys ( Catarrhina) have their nostrils close 
together and directed downward. Unlike the New World form, 
they have open cheek pouches. The tails are non-prehensile or 
absent. 

Macaques (Fam. Cercopithecidae) have cheek-pouches; range 
from one to three feet in length and are found in Asia. The pig- 
tailed monkey of the East Indies (a macaque) is trained to throw 
down ripe cocoanuts. The baboons {Cynocephalus)^ found in Africa 
and Arabia, are the fiercest of the Primates, explorers stating that 
hungry lions will not attack them. Their canine teeth are long and 
sharp. They go in troops of a score, robbing grain fields, but also 
feeding on birds. They are terrestrial but do not walk erect. The 
Asiatic holy apes (langurs) represent to the Hindoos, Hanuman, the 
Monkey God, who assisted Rama, a mythical hero. The pious 
Brahmins protect them so that they are great pests. The wanderoo 
of Ceylon and the Nose Monkey of Borneo are other interesting 
types. These forms have a sacculated stomach, in the first chamber 
of which leaves are stored for a time, obviating the necessity of 
cheek pouches. 

The anthropoid apes {Simiidae) assume an erect posture when 
they come to ground, although they are arboreal in their habits. 
They lack cheek pouches and ischial callosities (except in the 
gibbon). Their arms are much longer than the legs, they have an 
opposable pollex and a vermiform appendix. The gibbons {Hylo- 
bates)y the smallest of the man-like apes, are found in the Indo- 
Malayan region. They have long jaws with extremely long canine 
teeth and their arms are the longest of any of the group. They leap 
remarkable distances from branch to branch. Although naturally 
timid, they often exhibit surprising courage in the defense of their 
young. The Siamang of Sumatra is jet black and has a throat 
pouch that distends as the animal shrieks. The brown orang-utan. 



414 



MAMMALIA 



found in Borneo and Sumatra, lives in tree tops, but comes to the 
ground for water. It is easily tamed when young, but as it ap- 
proaches maturity becomes savage. It is about two-thirds the size 
of a gorilla, reaching a height of four and one-half feet. It sleeps 
in a nest of broken branches in the fork of a tree. 

The gorillas are the largest and most powerful of the monkeys. 
They have a tremendous barrel-like chest and massive frame and 
are able to aquit themselves with distinction in any battle. Since 




Fig. 234. Chimpanzee. (Courtesy of N. Y. Zool. Soc.) 

the time of Du Chaillu, gorillas have been regarded as most ferocious 
beasts. The late Carl Akeley believed however that the gorillas of 
Western Africa rarely attack man unless forced to a fight. Gorillas 
reach a height of six feet and weigh as much as five hundred pounds. 
The chimpanzee (Figure 234) is a third smaller than the gorilla and 
has a large brain and the keenest mind of any ape. It is easily taught 
and when young is quite popular with directors of animal films. 
The two species of chimpanzees are natives of equatorial Africa. 



MAMMALIA 



415 



Hominidae. — Man resembles the lower vertebrates in general 
characteristics and differs less in structure from the higher apes 
than do the monkeys. The Hominidae differ from the Simiidae 
chiefly in the development of the brain and in those characteristics 
associated with an erect posture. 

Among the most striking of the characteristics differentiating 
man are his increased brain development and power of articulate 
speech; reduced canine 
teeth, spinal column adapted 
to erect posture with four 
distinct curves; basin-shaped 
pelvis which supports vis- 
cera; arms shorter than legs 
and with opposable thumbs, 
arched (shock-absorbing) 
feet. Whether loss of hair 
has come from the wearing 
of clothes is a subject for 
conjecture. (Figure 235.) 

Fossil Man. — Human 
fossils are very rare, and 
when found are either in 
river valley deposits or in 
those limestone caverns that 
served as homes and later as 
burial places. 

The Java ape-man 
{Pithecayithropiis ei'ectiis) , 
consisting of a cranium, a 

femur and four teeth, was ^ — g 

discovered by E. Dubois in ^^^ ,_^^_ Skeletons of man and of gorilla, 
a river deposit at Trinil, (Lull. Courtesy of The Macmillan Co.) 

Central Java, in 1891. The 

age of the geological formation was estimated at about 500,000 
years (Early Pleistocene). The teeth were more human than in 
the gibbon and the skull capacity was about two-thirds that of 
man. Pithecanthropus erectus was about five feet, seven inches tall. 

The Heidelberg jaw, representing the oldest recorded European 
race {Homo heidelbergensis), was discovered in 1907 in a gravel pit 
seventy-nine feet below the surface, at Mauer, near Heidelberg, S. 





4i6 MAMMALIA 

Germany, by Dr. O. Schoetensack. The mandible was found fully 
equipped with teeth. 

The Piltdown man^^ {Eoanthropus dawsoni), found in 191 1 by 
Mr. Charles Dawson at Sussex, England, consisted of fragments of 
the cranial walls, nasal bones, a canine tooth and a mandible. The 
brain case was typically human except for the thickness of the walls. 
The forehead was high and lacked the prominent supraorbital ridges 
of the Neanderthal man. The jaw was apparently more apelike. 

The first specimen of the Neanderthal man was discovered in 
1856 near Dusseldorf in Rhenish Prussia. In a cavern high up on 
the side of a ravine an entire human skeleton was found, but it was 
at first thought to be an idiot soldier from an expedition of Napoleon. 
Later ten related skeletons were found in various places in Western 
Europe. They were short, the males reaching a height of only five 
feet, five inches. Neanderthal man is supposed to have lived during 
the third interglacial and fourth glacial periods. The Neanderthal 
people were cave-dwellers and made tools and weapons of flint. 
They buried their dead, leaving weapons and food for use in the 
future world. Whether they were destroyed or amalgamated seems 
debatable. One European Professor of Anthropology living a 
few decades ago was himself described as a " typical Neanderthal 
man." 

At Aurignac, France, seventeen skeletons of Cro-Magnon man 
were found in 1852, but were buried in the village cemetery and lost 
to science. In 1868 five more skeletons were discovered at Cro- 
Magnon, France, and shown to belong to a highly developed pre- 
historic people. Physically they were superb, some of them reach- 
ing a height of six feet, four inches. Their brain was larger than 
the average brain of the white race of today. Cro-Magnon men 
came from either Asia or Africa and replaced or absorbed the 
Neanderthal type. Along with them developed a high type of art 
as shown by bone and ivory carvings and cave paintings. Like 
the Neanderthal man their burial customs indicate a belief in life 
after death. Following the Cro-Magnons and perhaps absorbing 
them came migrants from Asia, establishing the narrow-headed 

" Osborn, H. F. 1929. Note on the geologic age of Pithecanthropus and Eoan- 
thropus. Science, vol. 49, no. 1782, pp. 216-217. Osborn states that Eoanthropus, 
the Piltdown man, is now believed to be of greater geologic age than Pithecanthropus 
of Java. 



MAMMALIA 4I7 

Mediterranean and the broad-headed Alpine types which persist 
today. 

The Peking Skull. — In December, 1929, Mr. W. C. Pei, who was 
in charge of excavations at Chou Kou Tien, near Peking, discovered 
the skull of a primitive man. It was possible to fix the age of the 
Peking Man at the beginning of the Pleistocene (Ice) Age. The 
brain was apparently advanced over that of the Pithecanthropus., 
and had a slight frontal bulge. Further study is being made, and 
should be most important since the cranium is complete. Pere 
Teilhard de Chardin and Dr. Davidson Black are engaged in study- 
ing the skull and in searching for eoliths. 

Races of Man. — We have chosen from the various classifications 
of Homo sapiens a division into three predominant varieties, the 
Negro, Mongolian and Caucasian, first describing the most primitive 
race now living, probably related most closely to the Negroid. 

The Australian race have a chocolate brown skin, long black 
wooly hair, a long skull (dolichocephalic), prominent eyebrows, large 
canine teeth and are tall with long limbs. They are still found in 
Australia and are the most primitive of living men. 

The Negroid race have a black or brown skin with short wooly 
hair, a dolichocephalic skull with flattened nasal bones, prominent 
sloping teeth and thick lips. They are found in Africa from the 
Sahara Desert to the Cape of Good Hope. 

The Mongolian race have a yellowish brown skin, straight black 
hair, scanty beard, a short head (brachycephalic), flat nose, small 
oblique eyes and teeth of medium size. They include the Chinese, 
Japanese, Tartars, Polynesians, Esquimos, North and South Ameri- 
can Indians, Lapps and Finns. 

The Caucasian race have a white skin, soft straight hair, a well- 
developed chin, thin lips, small teeth and a narrow nose. 

(«) The Mediterranean race are short, slender, long-headed with 
eyes and hair brown or black. Members of this race, found orig- 
inally along the shores of the Mediterranean, are ancestral to the 
slender and short-limbed brunets of the British Isles and the 
Continent. 

{h) The Alpine race are of medium height, round-headed with 
eyes gray or brown to black. The Central French, South Germans, 
North Italians, Austrians, many Poles, Turks, Armenians and 
Persians are of Alpine ancestry. 

(r) The Nordics are tall and long headed, with blonde hair, and 



41 8 MAMMALIA 

blue or gray eyes. They include the Scandinavians, North Ger- 
mans, many French and Dutch, English, Scotch, most Irish and the 
Americans and Canadians of early immigration.^ 

Race Mixture and the Evolution of Man. — While it has been 
demonstrated in some parts of the world that the offspring from the 
union of distinct races are of an excellent type, we are jealously 
guarding these United States against swamping our best stock with 
poorer lines, Caucasian though they may be. For many years it 
was common in some European countries to banish criminals and 
defectives, and even to furnish them transportation to the land of 
the free. Today we find judges in some of our states most gerter- 
ously warning petty criminals to get out of the state (and into 
another). But the stringency of our present immigration laws now 
prevents many undesirables from entering the country. 

Charles W. Eliot thought Zangwill's phrase the " melting pot " 
most inapplicable to America. He agreed with the one who sug- 
gested a new symbol — " America should be a symphony orchestra, 
playing with intelligence, good will, and self control." 

Mammals as Migrants. — Relatively few mammals migrate. 
Those that do migrate include the bison, reindeer, fur seal, dolphin, 
bat and lemming. The bison formerly ranged over North America 
from north to south about thirty-six hundred miles; from east to 
west about two thousand miles. The reindeer of Spitzbergen mi- 
grate to the central portion of the island in summer and back to the 
sea coast in the autumn, where they feed upon sea weed. Fur seals 
breed on the Pribilof Islands in the Bering Sea, from about May i to 
September 15. Then they go out to sea and spend the winter, 
making a total circuit of about six thousand miles. The dolphin 
travels up the Amoor River for four hundred miles just as the ice 
breaks up. Bats have seasonal migrations of considerable distances. 
The lemmings of Norway and Sweden are small rodents (relatives of 
the mice) about three inches long. Periodically the increase in 
their numbers is so great that they migrate down from the moun- 
tains and traverse the Scandinavian Peninsula in hordes. It is 

1 Brouzas is studying the physical characteristics of the ancient Greeks. He 
reports that Inge beheved the Spartans were almost pure Nordics, and the Athe- 
nians ahnost pure Mediterraneans. Brouzas holds that the principle of like attracts 
like must be accepted, and that the Greeks admired blond hair because they them- 
selves were blond. (Consult Brouzas, C. G., 1930, Proc. Amer. Phil. Assoc, vol. 
61, pp. xxvi, xxvii.) 



MAMMALIA 419 

traditional that they devour all the vegetation in their pathway, 
and continue to travel overland and across streams until they reach 
the sea where they perish. If it were not for their enemies, the 
Arctic foxes, weasels, and lynxes, they would ruin the territory 
through which they pass. 

Homing Instinct. — Many instances are cited indicating the 
remarkable ability of the common house cat and the dog to find 
their way home after having been transported by train or automo- 
bile. Undoubtedly the roving habits of both these animals have 
given them a rather wide knowledge of adjacent territory. It is 
most difficult, however, to conceive of their finding landmarks a 
hundred miles away. 

In the savage state, man evinces an uncanny ability in travelling 
through forests and swamps, and emergencies have proved to many 
a city dweller that he has a well-developed, although unused ability 
in that line. Keen, though unanalyzed, powers of observation 
prove to be the solution of many unexpected achievements in the 
wilds. 



CHAPTER XX 



Mammalia — Physiology 



Man is an animal. We see this more and more as we study the 
structure and vital phenomena of other animal organisms. Co7n- 
parative Anatomy shows the structure to be comparable and animals 
have been grouped in a series ranging from the simple one-celled 
animal to man in all his complexity. Embryology shows us that man 
conforms to the Law of Development just as inflexibly as does the 
simplest invertebrate. Comparative Embryology shows a striking 
similarity between the embryo of man in its early stages and the 
embryos of other mammals at corresponding periods in their devel- 
opment. But it is in the study of the vital phenomena, Physiology, 
that we find the greatest similarity. There is a wide variation in the 
degree of specialization of organs for certain functions, but there is 
in all living animals a property that separates them from the non- 
living by a seemingly unbridgeable chasm. 

The late Jacques Loeb, of the Rockefeller Institute, artificially 
fertilized the eggs of the sea urchin and the starfish by chemicals, 
and to his great disgust, the reporters announced that he had pro- 
duced life. Jarring, varying temperatures, and differences in the 
salinity of the water produce the same effect in Nature. All 
sciences have theories regarding the origin of life, but no theory is 
without a flaw. Granting that chemicals can be combined to pro- 
duce life, we have proved nothing. We have pushed back the ques- 
tion a little farther. We have not shown the nature of the phenom- 
enon which causes the chemicals to combine. This is life perhaps. 
Electricity may be life in one sense. However, we cannot prove the 
spontaneous generation of life. We are able to vary conditions in 
the case of developing eggs and get different results but we cannot 
introduce the spark of life. Lovatt Evans said (1928) in his address 
before the British Association for the Advancement of Science: 
" Science can not fathom the mystery of life." 

Man vs. the Higher Apes 

In man and the higher apes the similarity of structure is carried 
out even to the finer details of the brain. The brain weight and 

420 



MAMMALIA— PHYSIOLOGY 421 

histological development of the cerebral hemispheres in the higher 
apes is about that of a microcephalic idiot. The behavior of the 
apes shows many human traits in that capacity for learning and 
intelligent acts can be interpreted. 

The work of Yerkes (" Almost Human ") and of Kohler has 
shown the ability of the chimpanzee, and to a less extent the gorilla, 
to recognize complex relations in problems set the animals and has 
indicated a capacity to plan solutions and to utilize simple tools. 

Man has developed a remarkable reasoning power and has 
brought with him a high development of conscience and a religion. 
Even the most degraded savage worships something. The dis- 
coveries of archaeologists show that wherever human remains are 
found, tokens of idol or deity worship accompany them. 

Man is continually at warfare with other animals and with his 
fellow men. As man's religion and sympathy become more strongly 
developed we find that his attitude towards gaining possessions by 
aggressive warfare decreases.^ 

It is necessary for the life of any organism that it be properly 
adjusted to its environment. The more plastic the mind, the more 
easily does life continue. The very process of education tends to 
keep the mind open and to prolong the period of mental adolescence. 

Physiology of the Vertebrate Animal 

In the vertebrate type of animal we distinguish from a physio- 
logical point of view the following principal organs: those of diges- 
tiorty respiration^ circulation^ excretion^ reproduction^ muscular system, 
which is the organ of movement, and the nervous system, the organ 
of control. 

The body is made up of a bony framework, the skeleton, with 
muscles and fat covered with skin. Food is taken into the mouth, 
digested by the alimentary system, the wastes are carried off by the 
excretory system, the lungs and the skin, and the sustaining portions 
are carried around to the tissues by the ^/oo^ which brings the wastes 
from the tissues to the excretory system. The lungs serve to aerate 
and purify the blood before its return to the organs of the body. 
The interdependence of the various systems calls for a governing and 
correlating center, the nervous system. It is constantly functional in 

1 " The human animal cannot be aware of beauty except in self-forgetfulness, and 
it cannot produce beauty except in self-forgetfulness." Arthur Clutton-Brock. 



422 MAMMALIA— PHYSIOLOGY 

bringing about rapid readjustments to external conditions, as well 
as in keeping the natural relations between the systems and organs. 
The organs of digestion include the alimentary canal and its accom- 
panying secretory glands, the liver and pancreas, which have as 
their function the preparation and absorption of foodo 

The organs of respiration comprise the lungs and skin. Their 
function is the exchange of gases between the organism and the 
atmosphere. The organs of circulation are the heart, arteries, veins, 
and capillaries with fluid contents. Their function is distribution 
and renovation of blood throughout the organism. The muscle fiber 
is the essential element of this system. The main organs of excretion 
are the kidneys, which are supplemented by the action of the lungs, 
the skin, the liver and the blood. Their function is the separation 
of urea from the blood. The active element is the epithelial cell. 
The organs of reproduction are the ovaries and the testes. The essen- 
tial elements are the ovum and the spermatozoan, both of which 
are derived originally from epithelial cells. 

The muscular and nervous systems form an organ which is both 
master and servant to the entire organism. The nerve centers 
receive information through the sense organs and nerves regarding 
the outer and inner needs of the entire organism and, acting through 
the motor nerves^ bring about muscle activity producing those move- 
ments that satisfy the demands of the situation. 

The principal nerve centers are the brain and spinal cord. The 
principal sense organs are the skin, eye, ear, nose and tongue. 
Many of our most important body functions are carried on, without 
fret or worry, by the sympathetic system. 

Mammalian Physiology 

External Anatomy and Locomotion. — For the most part the 
mammals are quadrupedal in locomotion. Even in man, the biped, 
whose upright posture has been fashionable for ages, it has been 
shown that resumption of the quadrupedal method of locomotion 
may benefit cases of prolapsed viscera. 

The plantigrade animals like man and the bear are usually five- 
toed. The digitigrade forms such as the cat are four-toed. In the 
horse, a digitigrade or unguligrade animal, the original four toes 
(with a rudimentary fifth) have degenerated to a single toe. The 
horse and the antelope seem particularly adapted for speedy flight. 



MAMMALIA— PHYSIOLOGY 423 

Most jTvam-mals except the ungulates have a perfected digitigrade 
gait, having developed special sole-pads for the absorption of the 
shock. The elephant^ however, is said to be rectigrade, its weight 
resting on heavy pads, the foot not moving independently. In the 
camel^ the feet are provided with two broad cushion-like pads, while 
the hoofs are reduced to nails. 

The only tvuQ flying mammals are the bats, but other forms, such 
as certain squirrels, are able to plane through the air. Extensions 
of the skin on the inside of the fore and hind limbs are drawn taut 
when the limbs are extended, and furnish a flat surface. 

Some forms like the mole and the gopher are able to burrow in 
the ground. In these forms, particularly in the mole, one finds 
heavily developed shoulder girdles. Depending on the degree of 
subterranean life, one finds degeneration of the eyes. 

Certain aquatic mammals such as the whale have undergone 
degeneration of the hind limbs, with a great development of the 
pectoral appendages for swimming. In marine mammals, we find 
that the caudal fin is horizontal instead of vertical and that it has 
two symmetrical halves. 

C&nfro/ bodies CcenfrosomK) 



Oc^g, 6o<:/,B^l,-^y ^ Vc^^Z/co/ layer 

PJosmosame or true nucleo/us "^~-T-^ *'j-ii"'A^ ^ *^'r"1 



Chromatin "T Tfeul^itSiiSr; -■.*:- -14 Plasfids 

Linin 




'■^Truc trva/f or membrono 



Korvosome or chromatin- nucleolus It-': < ^ , ^ 'a « ^ '•ri ^ . . 

Vacuole ff/tjid <^obule) 

- Passive metaplosmic or 
paroplaatic bodies 

Fig. 236. Diagram of a generalized cell. (After Wilson, The Cell in Development and 
Heredity. Courtesy of The Macmillan Co.) 

Histology. Cells and Tissues. — All living bodies are composed 
of organic constituents called cells. In the Metazoa we find one 
fundamental characteristic, that of division of labor. Certain cells, 
grouped together for the purpose of reproduction, are called germ 
cells, while others which carry on all processes except reproduction 
are called somatic cells. The argument between the Lamarckian 
and the Weismannian schools is based upon the question of possible 
influence of environment upon the germ cells. (See page 514.) 
(Figure 236.) 



424 



MAMMALIA— PHYSIOLOGY 



A cell is a minute portion of living substance or protoplasm, 
sometimes inclosed by a cell membrane, and at some stage of its 
development containing a nucleus. It is a physiological unit. 
(See page 423.) 

When cells, similar in structure and originating from the same 
germ layer of the embryo, are grouped together to perform some 
special function, they are called tissues. 




Fig. 237. Four nerve cells. J and C, from the cerebellum; B, from the gray- 
matter of the spinal cord; D, from the cerebrum; a, the axon. The cells J and D are 
stained so that the main body and the dendrites (p. 76) are a uniform black; B and C, 
so as to show the nucleus and cytoplasm. (Hough and Sedgwick, The Human Mecha- 
nism. Courtesy of Ginn and Co.) 

We may classify tissues as Epithelial or bounding tissues, and 
Connective or supporting tissues. E-pithelium is a tissue which is 
distinctively cellular with its cells usually similar in size and form, 
and united by a small quantity of intercellular substance. (Figure 

237-) 

Epithelium is found covering all outer surfaces and all inner 

free surfaces and is protective and secretory. It is the first tissue 

found in the embryo. Pavement epithelium is found lining the 

mouth, on the inside of the lungs, and covering the body. It is 



MAMMALIA— PHYSIOLOGY 



425 



constantly being worn off and replaced. Cubical epithelium is 
found in the bronchioles of the lungs and in the ducts of certain 
glands of the digestive system. Columnar epithelium is found 
lining the alimentary canal of vertebrates and a peculiar type of 
" ciliated " columnar cell is commonly found in the trachea and 
bronchi and lining the oviduct and the central canal of the spinal 
cord. Glandular epithelium consists of epithelial cells so differen- 





1A 



2A 




Fig. 238. Diagram illustrating different forms of glands. Upper row, tubular 
glands; /, 2, and J, simple tubular glands; 4, compound tubular gland. Lower row, 
alveolar glands; /a, 2a, and Ja, simple alveolar glands; 4a, compound alveolar gland. 
(From Bailey's Histology. Courtesy of Wm. Wood and Co.) 

tiated as to be capable of forming compounds given off as secretions. 
The simplest type of glandular cell is the unicellular gland called the 
" goblet " cell. This type of mucus-secreting cell is found in the 
hypodermis of the earth worm and occurs also in the intestines of 
vertebrates. N euro- epithelium is found lining some of the ven- 
tricles of the vertebrate brain. Certain cells are aggregated into 
end organs of special sense. The sensory cells are spindle-like with 
hair-like processes extending as fine fibers at the inner end and 
establishing connection with the nerve. Ordinarily these cells are 
surrounded by supporting sustentacular cells. Germinal or repro- 
ductive epithelium is found in the gonads. The sexual cells arise 



426 MAMMALIA— PHYSIOLOGY 

from epithelium derived from the primitive mesoderm or in some 
cases from ectoderm or endoderm. When the sexual cells develop 
(somewhat as glands form) they frequently starve the adjacent cells. 

Connective tissues are derived from the mesoderm. Mucous 
tissue is found in embryonic animals. The umbilical cord and the 
vitreous humor of the eye are mucous tissue. Reticular tissue is 
fibrous connective tissue in which the inter-cellular substance has 
disappeared. It is found in adenoid tissue and in lymph glands, 
in the spleen, and in the mucous membrane of the intestinal canal. 
Fibrous tissue consists of areolar, tendinous and elastic tissue. 
{a) Areolar tissue consists of bundles of white fibers with a few 
fibrils of elastic tissue. The inter-spaces are filled with lymph. 
{h) Tendons and ligaments consist of dense white fibrous tissue. (<r) 
Elastic tissue consists of yellow elastic fibers, frequently found in 
bundles. 

Adipose tissue consists of a matrix of areolar tissue containing 
cells, the nuclei of which are a-central. 

Cartilage may be hyaline, elastic or fibro-cartilage. {a) Hyaline 
cartilage is jelly-like and found in embryonic bones and at the ends 
of bones. It has a homogeneous matrix and prominent cells. {]?) 
Elastic cartilage is found in the lobe of the ear, in the epiglottis and 
in the Eustachian tube, {c) Fibro-cartilage is found in inter- 
vertebral substance and in the sesamoid bones. It consists of 
groups of slightly flattened nucleated cells enclosed in capsules and 
scattered among fibers. 

Bone. — Bony tissue may be either compact and dense like ivory 
or spongy and cancellous with many interstices. The outer layer 
is called t\\Q periosteum. In true bone we find fine fibers in a calcified 
ground substance with branched cells, the bone corpuscles., lying in 
cell spaces called lacunae situated in folds or lamellae around a cavity 
called the Haversian canal. Ramifying passages which contain cell 
processes are called canaliculi and radiate in all directions from the 
lacunae. 

Muscle substance is a specialized contractile tissue which is the 
agent of active movement. It is distinguished from undifferen- 
tiated protoplasm since it contracts in one direction. In inverte- 
brates such as protozoa, sponges, and coelenterates we find primitive 
contractile fibrils, but in worms, molluscs and arthropods, muscular 
tissue is highly developed. Non-striated or smooth 7nuscle cells 
are involuntary. The cells are long, spindle shaped, and somewhat 



MAMMALIA— PHYSIOLOGY 427 

flattened. Each cell has an oval or rod-shaped nucleus. The cell 
substance is longitudinally striated but has no cross striations. It is 
found in the walls of the intestine, trachea, and bronchi, the urino- 
genital system, blood vessels and hair follicles of mammals and in 
the foot of the mollusc. Striated muscle consists of long cylin- 
drical fibers made up of fibrils arranged end to end in small bundles 
and enclosed by a sheath or sarcolemma. This outer connective 
tissue covering is continued into tendons which attach to the skele- 
ton. Nuclei are situated in the liquid protoplasm under the sar- 
colemma. The striated appearance is due to the presence in muscle 
substance of different chemical compounds of protoplasm arranged 
in light and dark bars which give a different staining reaction. It is 
supposed that the wider bar is the contractile substance. 

Cardiac muscle is a peculiar type of involuntary striated muscle. 
The fibers consist of primitive fibrils which are aggregated into 
oblong masses each with a nucleus in the center. Muscles are well 
provided with nerves and blood vessels. In cardiac muscle inter- 
cellular bridges are found. (Clark, 1927.) 

Skin. — The skin covers the body completely, the epithelium 
changing at the openings of the internal passages to a soft delicate 
mucous membrane. It varies in thickness, becoming extremely 
heavy in man on the palms of the hands and the soles of the feet. 
In the cat it is well developed on the pads of the feet and in the 
neck region, where it is protective against the bites of enemies. 
The skin consists of the epidermis, cuticle or outer skin, and the 
dermis, corium or true skin. 

The epidermis consists of two layers, the stratum Malpighi and 
the horny layer, or stratum corneum. Although bony plates are 
lost in the mammals, one finds heavy armor in some forms, the 
rhinoceros having a skin over three inches thick. The dermis^ 
cutis vera or true skin, consists of fibrous connective tissue with 
many glands, blood vessels, lymphatics and nerves. The append- 
ages of the skin are the nails, and the hairs, with their sebaceous 
glands and sweat glands. They are all developed as thickenings 
and down growths of the Malpighian layer of the epidermis. The 
sebaceous glands are small saccular glands, the ducts from which 
open into the mouths of the hair follicles. Both the ducts and the 
saccules are lined by epithelium which becomes charged with fatty 
material. The sweat glands, so well developed in terrestrial forms, 
are much reduced in aquatic mammals. 



428 MAMMALIA— PHYSIOLOGY 

Claws or Nails. — Claws or similar structures, nails or hoofs, are 
found in all the mammals except the Cetacea. They are thickenings 
of the epidermis. In the cat there are five claws on each fore foot 
and four on the hind foot. The dermis forms a crescentic fold at 
the root of each claw. 

Hair. — All mammals are born with a thin covering of very fine 
hair, lanugo. It can be noted on a child from the day of birth to 
two or three days of age, when it disappears. It is replaced by a 
protective covering of more noticeable hair, as the child grows older. 
The cat has long coarse hairs on each side the nose called vibrissae^ 
which function as tactile organs. In the marine mammals, although 
fetal hair appears, the majority have lost their hair, except for a 
few bristles around the mouth. The fur seals retain a thick under 
coat of fur — " seal skin." In the white whale and the narwhal, even 
the fetus has lost its hair. Those mammals without hair develop 
a thick layer oijat under the skin. The skin is richly supplied with 
tactile and temperature perceiving corpuscles. 

Perspiration. — The body is continually throwing off perspiration 
which we term insensible perspiration. Excessive amounts appear- 
ing as droplets are termed sensible perspiration. In man, the in- 
sensible perspiration is estimated to be from one to two quarts in 
twenty-four hours. Increased exercise, pilocarpin, strychnin, 
nicotine, nausea or mental excitement will increase perspiration 
markedly. 

In the dog and the cow with perspiration limited by the nature of 
their skins, we find that the muzzle shows evidence of considerable 
evaporation. In the horse, it is estimated that about fourteen 
pounds of insensible perspiration are extruded in a day, through the 
skin, of course. 

Digestive System. Mouth. Teeth. — Mammals have two sets 
of teeth, the deciduous or milk teeth, and the permanent teeth. 
The whalebone whale has a fringe of baleen hanging down from the 
upper jaw and acting as a strainer for the small fish and Crustacea 
eaten by these monsters of the deep. The duck-mole {Ornithorhyn- 
chus) has its teeth composed of thick strong plates. 

Salivary Glands. — The mammals possess parotid, submaxillary 
and sublingual glands. These glands are serous, mucous and mixed, 
but in some animals the submaxillary is mucous and the sublingual 
is mixed, while in others the reverse is the process. Salivary glands 
are lacking in the Cetacea. The vampire bat has a buccal gland 



MAMMALIA— PHYSIOLOGY 



429 



secretion that prevents the clotting of blood. In man, the watery- 
secretion from the parotids contains the enzyme ptyalin^ while the 
submaxillary and sublingual glands furnish the viscid mucin. 
The salivary glands and the mucous glands lining the buccal cavity 
furnish about three pints of saliva in twenty-four hours. 




Fig. 239. Section of a portion of a salivary gland, magnified 500 diameters. The 
duct d divides into the two branches d' and d'\ one of which ends in the alveoli, a, a. 
Neighboring alveoli, a', «', whose ducts are not in the plane of the section, are also 
shown. (After Koelliker. From Hough and Sedgwick, Human Mechanism. Cour- 
tesy of Ginn and Co.) 

Tongue. — The mammalian tongue is well supplied with tactile 
and gustatory papillae. The human tongue has three kinds of 
papillae. The filiform papillae are the smallest and are scattered 
over the dorsal surface of the tongue except at its base. In the 
Carnivora the conical tips of these papillae are heavily armed with 
horny epithelium, so that it is possible by their use to scrape bones 
clean of muscles and even tendons. There are about four hundred 
fungi-form papillae found over the middle and front of the tongue. 
They are bright red in color. The ariterior portion of the tongue 
is sensitive to sweet substances., while the lateral portions are sensitive 
to sour and salt. The circumvallate papillae, about twelve in num- 
ber, lie near the base of the tongue in a v-shaped group. They are 
richly supplied with nerve fibers and specialized sensory cells and 
are especially sensitive to bitter substances. 

In the mouth the food is divided, moistened, formed into a ball 
and prepared for swallowing. Some of the starch, acted upon by 
ptyalin, the enzyme of saliva, is changed into maltose. 



43° 



MAMMALIA— PHYSIOLOGY 



The esophagus is similar in structure to the pharynx but with 
well-developed mucous glands secreting an oily fluid that lubricates 
the canal. In man, it is about nine inches long. 

Stomach. — The mammalian stomach is divided into three dis- 
tinct regions, the cardiac at the anterior end, the intermediate 



Nosal covify — 
Pa/of e - 
Tongue - 



I -Mf -flaso- pharynx 

■ Cavity of moui'h 
■-Pharynx 

■-Openina of larynx 



Oesophagus 
Go// b/oddei^ 



, Pylorus 



Bi/e duct— 

Tr-ans\/erse co/on — 
Li\/er -- 



Hepatic flexure 
of colon 

Common orifice of b. 
and pancreatic duc/s 

Duodenum 

Ascend ina colon 

Caecum 

Appendix 
Ileum 




- Pancreatic duct 

^Splenic flexure 
' of colon 
Pancreas 



Descendlncj colon 



-r Small intestine 



Fig. 240. General view of the digestive system. (Cunningham, D. J., Textbook of 

Anatomy. Y. J. Pentland, Pub.) 

fundus and the pyloric at the right or intestinal end. A well- 
developed pyloric sphincter muscle is situated at the entrace to the 
duodenum. The acidity of the chytne^ when it reaches the pyloric 
region of the stomach, induces the sphincter to open. In adult 



MAMMALIA— PHYSIOLOGY 431 

man the stomach is about ten inches long, four inches wide and 
deep, and holds about three pints. 

Gast7-ic juice is a pale yellow fluid, rich in HCl. It arrests the 
process of changing starch to sugar, producing chyme. It contains 
pepsin^ which changes albumen and gelatin to a soluble form called 
peptone; rennin, which curdles milk; and lipase^ which emulsifies 
neutral fats and fatty acids, but has no effect on non-emulsified fats. 

Digestive Action in the Stomach. — The action of the saliva upon 
starch is arrested, and the larger lumps of masticated food are 
broken up into a thick, grayish soup-like chyme which consists of 
starch unchanged by saliva; oils and fats set free in the gastric 
digestion; undissolved proteins; dissolved proteins; and debris of 
indigestible materials such as cellulose. 

The small intestine consists of the duodenum situated on the 
right side of the body with a wide curve embracing pancreatic 
and bile ducts., t\\& jejunufn situated on the left side, and the some- 
what constricted ileum which leads to the cecum and the large 
intestine. The human small intestine is twenty-three feet in length. 

The semi-digested acid food from the stomach, as it passes over 
the bile duct, causes a flow of bile and pancreatic juices which tend 
to neutralize the acid chyme, but the contents of the duodenum do 
not become distinctly alkaline until they have reached a point at 
some distance from the pylorus. The valve of the common duct is 
closed when the chyme is rendered alkaline, and is opened when the 
acid chyme arrives again. 

The liver is of a dark red-brown color, situated just below the 
diaphragm. It is the largest gland in the body. The principal 
function of the liver is the formation of glycogen, sometimes called 
" animal starch." The glycogen is given out into the blood in the 
form of dextrose, into which it is changed by an enzyme in the hepatic 
cells. The liver thus acts as a reservoir for food, storing it up when 
it is in excess and expending it gradually to tide over periods of 
fasting. The liver forms bile and urea and is most important in the 
purification of the blood. The gall bladder, present in the cat as in 
man, is not found in all mammals, some rodents lacking it entirely. 
It stores up the bile and liberates it periodically, through the bile 
duct which enters the anterior portion of the duodenum as the com- 
mon bile duct, together with or close to the pancreatic duct. The 
liver weighs between three and four pounds in man and secretes 
nearly three pounds of bile in twenty-four hours. Bile is alkaline, 



432 MAMMALIA— PHYSIOLOGY 

greenish yellow In color and bitter to the taste. It is passed from 
the bile duct to the duodenum, where it neutralizes chyme and thus 
facilitates the action of the pancreatic juice. In higher vertebrates, 
bile has a weak ferment that acts on fats, aiding in their emulsifica- 
tion. It has slight amylotic and proteolytic ferments. American 
packing houses sell gallstones from cattle to the Chinese and Japanese 
who use them as medicine. 

The pancreas is a rather long narrow organ, pinkish-yellow in 
color and situated at the posterior end of the stomach, extending 
along its greater curvature. A duct traversing the gland enters the 
duodenum via the common bile duct or quite close to it. The 
pancreas secretes digestive enzymes and is also responsible for an 
internal secretion which regulates the liberation of sugar from the 
liver. (See p. 445.) 

Pancreatic juice is alkaline, its sodium carbonate neutralizing 
the acid food from the stomach. The enzyme trypsin is at first 
secreted in the form oi trypsinogen and converted into trypsin by the 
action of enterokinase formed by the intestinal glands. Trypsin 
converts proteins into amino-acids which are reconvertible into 
proteins when needed. Amylopsin {diastase) digests carbohydrates, 
thus continuing in an alkaline medium the action of the salivary 
glands stopped by the acid gastric juice of the stomach. Steapsin 
{lipase) splits fats into soaps, fatty acids and glycerine. Dissolved 
fats are absorbed in the intestinal walls and later combined to form 
fat in the cells. 

The human pancreas secretes about one pound of pancreatic 
juice in twenty-four hours. In the pancreas of the cow, which 
weighs but seventeen ounces, eleven pounds of fluid are secreted 
per day. 

Digestive Action in the Small Intestine. — The change of starch 
into sugar is resumed; proteins are largely dissolved by the action 
of the bile, pancreatic juice, and the intestinal juices. Starch is 
converted into sugar and the sugar is in part converted into lactic 
and other acids. Fats are emulsified and to some extent saponified 
by the steapsin of the pancreas. 

The Cecum. — x^t the point where the ileum joins the large 
intestine there is a pouch, the cecum^ relatively small in the cat and 
man, but large in herbivores, where cellulose is dissolved by bacterial 
action. In man, the cecum has attached to it an attenuated vermi- 
form appendix^ frequently the seat of inflammation. Foreign sub- 



MAMMALIA— PHYSIOLOGY 433 

stances, impacted feces, or parasitic worms, such as the pin-worm 
(see p. 90), cause appendicitis. 

The Large Intestine is divided into the ascending colon, the 
transverse colon, and the descending colon which terminates in the 
rectum. In the carnivora the large intestine is short; but is well 
developed with sacculated walls in the herbivora. The human large 
intestine, five feet long, is estimated to absorb four hundred cubic 
centimeters of water in twenty-four hours. 

Digestive Action in the Large Intestine.— The contents become 
slightly acid due to the fermentation of the contents of the intestine. 
Beneficial bacteria are very important. Absorption is very active. 
The great absorbent vessels are the veins and lacteah. The lacteals 
carry chyle to the thoracic duct at the receptaculum chyli. Food 
passes through the digestive tract of man in a few hours, but takes 
three days in the horse and five days in the cow. 

Digestion in the Ruminant (Example: the cow). — The cow lacks 
incisor teeth on the upper jaws and is therefore unable to cut it as 
she feeds, but rips loose a tuft of grass by pressing the lower incisor 
teeth against the upper jaw and giving a jerk of the head. After 
rolling the morsel between the molars a short time it is swallowed 
down the esophagus to the rumen or paunch. 

The stomach of the cow is large, occupying three-fourths of the 
abdominal cavity, and holds 45 gallons. It consists of four parts, 
the rumen^ the reticulum^ and the omasum^ constituting the pro- 
ventriculi; while the abomasum or " rennet " is the true stomach. 

The esophagus opens into the stomach on a dome formed by the 
rumen and the reticulum and is continued through the reticulum to 
the omasum by esophageal grooves. 

The rufnen is partly divided into dorsal and ventral sacs. Large 
papillae, sometimes reaching a height of one-fourth inch, stud its 
brownish mucous membrane. The muscular coat reaches a thick- 
ness of one inch. The food is stored in the paunch till a favorable 
time for rumination after which it is passed into the reticulum. 

The reticulum, or honeycomb, is the smallest of the four parts 
and contains mucous folds one-half inch high enclosing four, five and 
six-sided spaces (honeycomb) as well as many small papillae. At 
the reticulo-omasal orifice, there are small horny papillae, curved 
like birds' claws. The muscular coat has two oblique layers. Little 
balls of food are prepared in the honeycomb cells and then regurgi- 
tated for thorough mastication and mixture with the salivary secre- 



434 



MAMMALIA— PHYSIOLOGY 



tions. The cow moves her lower jaw once in one direction and then 
chews the other way. Subsequent to mastication the food is swal- 
lowed again and passes through rumen and reticulum to the omasum 
or psalterium. 

The omasum or psalterium, sometimes called " the maniplies," 
has loo longitudinal folds or laminae which spring from its dorsal 
and lateral walls. A dozen of the largest have a convex attached 
edge and a free concaved ventral edge. The food is pressed into 



ReHculum 



Abomasum 




Dorsal sac -4 



—;/■ Duodenum 

' Posterior blind sacs 

Fig. 241. Stomach of a ruminant. (Drawn by W. J. Moore.) 



thin layers in the spaces between the laminae and reduced to a fine 
state of division, by being ground down by minute horny papillae 
studding the surface of the folds. From the omasum the food passes 
into the true stomach. 

The abomasum^ or true stomach, is divided by a constriction into 
two regions, the fundus and the pylorus. It has a mucous coat and 
longitudinal and circular muscles, strongly developed to form the 
pyloric sphincter. In the abomasum the acid gastric juice functions 
as in other mammals. 



References on the Ruminant Stomach 

Reynolds, M. H. 191 i. Veterinary Studies for Agricultural Students. 

Macmillan and Co., N. Y. 
ScHALK, A. F., AND Amadon, R. S. 1928. PHysiology of the Ruminant 

Stomach. Bull. 216, North Dakota Agr. Exp. Sta., Fargo, N. D. 
SissoN, S. 1914. Anatomy of Domesticated Animals. 2d ed. W. B. 

Saunders Co., Phila. 



MAMMALIA— PHYSIOLOGY 435 

Chemical Characteristics of Protoplasm. — When we attempt an 
analysis of the chemical constituents of living protoplasm, we induce 
important changes. By weighing the material before treating it, 
and then comparing the weights of all substances determined, we 
find that it is possible to learn most of the constituents, except that 
all-important one — life. Protoplasm consists of proteins, carbo- 
hydrates, fats, inorganic salts, enzymes, water and the " vitamins." 

Proteins are compounds with high molecular weights, which 
contain carbon, oxygen, hydrogen and nitrogen. Usually the/ 
contain sulphur, and sometimes phosphorus. They are apparently 
a condensation of the molecules of numerous amino-acids and by 
hydrolysis they yield amino-acids in different quantities and of 
different characteristics. 

Proteins differ in their color reactions and are readily classified 
by such reactions. Proteins also differ in precipitation reactions. 
Some are precipitated by the mineral acids such as nitric, hydro- 
chloric, and sulphuric, others by salts of the heavy metals, par- 
ticularly mercuric salts. The alkaloidal reagents which precipitate 
the vegetable alkaloids are precipitants for proteins. Eggs, rich in 
proteins, are used as an antidote for copper, lead or mercury poison, 
since they render the metallic compounds insoluble so that they 
may be removed by the stomach-pump or laxatives. 

Colloids. — Proteins are colloids. The term " colloid " which 
comes from the Greek word for " glue " referred at first to substances 
like glues and gums, but now is used to indicate finely divided mat- 
ter suspended in any medium. Colloids may include liquid dis- 
persed in a gas or another liquid or even a solid; or may refer to 
solids similarly dispersed. Blood, lymph, bile and the various 
digestive secretions are common examples of colloidal solutions. 

Proteins, as colloids, do not readily diffuse through membranes 
nor go into solution They readily absorb substances however and 
in the cell they synthesize and oxidize them. Protein individuality 
is such that the blood of one order cannot, as a rule, be transfused 
successfully into the circulation of another order without fatal 
results. Foreign proteins are apparently incompatible. It is 
interesting to note, however, that human blood may be successfully 
administered to certain of the anthropoid apes. Clumping together 
(agglutination) of blood corpuscles occurs when incompatible blood 
is transfused. 



436 MAMMALIA— PHYSIOLOGY 

Precipitin Reaction. — An interesting test for the detection of 
human blood in murder cases is dependent on the solubility of blood 
protein. It is said that soluble protein will give the test after a 
period of fifty years. The serum of an animal (a rabbit is ordinarily 
used), injected with the blood or blood serum of another animal, will, 
when added to a homologous serum, precipitate the albumin in the 
form of a light flocculent precipitate. (See p. 528, Evidence for 
Evolution.) 

Carbohydrates consist of carbon, hydrogen and oxygen, and occur 
in both the crystalline and colloidal state. Carbohydrates can be 
converted into fats. In plants the starches are commonly dis- 
tributed, but glycogen is the only example of animal starch. Gly- 
cogen occurs in all the growing cells of the animal body, but is 
found chiefly in the liver and muscles (see page 444). 

There are three chief groups of carbohydrates. The monosac- 
charids with one sugar group include dextrose or grape sugar. The 
disaccharids include cane sugar, milk sugar and maltose. Several 
monosaccharid molecules become united into a polysaccharid. Corn 
and potato starch and wheat flour are common examples of polysac- 
charids. The monosaccharid, dextrose (C6H12O6), is formed in the 
leaf of a green plant from carbon dioxide and water. Plants manu- 
facture carbohydrates from carbon dioxide and water. Recently 
Professor E. C. C. Baly of Liverpool University has produced sugar 
synthetically in his laboratory by utilizing ultra-violet rays on quartz 
vessels of water in which carbon dioxide was dissolved. With small 
quantities of either iron or aluminium compounds as catalysts (see 
page 440) he obtained sugar. In nature, sugar is made through the 
action of the sun on chlorophyll-containing plant cells, and from this 
sugar other foods are formed by the addition of different chemical 
elements. Sugar, then, is the source of all food, and the process 
just mentioned, " photosynthesis," is the most important chemical 
reaction in nature. 

Fats contain carbon, hydrogen, and oxygen in different propor- 
tions, containing much less oxygen in proportion to the carbon than 
in the carbohydrates. Fats can readily be converted into carbohy- 
drates. They are found in seeds and nuts, and in animals occur in 
the connective tissue called adipose. Lipins contain carbon, oxy- 
gen, hydrogen, and nitrogen, and may contain phosphorus also. 
The lecithin of egg yolk is an example of a lipin. Fats of the body 
are derived not only from the fatty substances consumed, but are 



MAMMALIA— PHYSIOLOGY 437 

also formed from carbohydrates and proteins. Fats contain twice 
as much heat energy as carbohydrates and are essential in maintain- 
ing the proper body temperature. 

Substances that contain at some point in the chain two carbon 
atoms united by more than one bond are said to be " unsaturated," 
and are able to form additive compounds with the halogens chlorin, 
bromin, and iodin. The " iodin number " of an oil or fat is a meas- 
ure of its ability to absorb iodin. Unsaturated fats act antienzy- 
matically, and undoubtedly function in the animal body in taking 
up iodin. Excess fat in the diet may predispose to goiter. 

Experiments by Chidester and associates have indicated the 
importance of unsaturated fatty acids in the treatment of Vitamin A 
deficiency, when combined with ferrous iodide. The author is also 
continuing experiments with the idea that the efficacy of wheat 
germ oil, hempseed and other oils used in the recovery of animals 
deficient in Vitamin E is in part due to their highly unsaturated 
condition. The degree of unsaturation decreases rapidly in seeds 
during their period of germination. Cocoanut oil has a high degree 
of saturation, and is ineffective. 

Chemical Elements of Protoplasm. — Carbon compounds are the 
primary materials of protoplasm. Carbon unites with oxygen to 
form carbon dioxide and water and to liberate energy. 

Hydrogen is taken into the bodies of plants and animals in com- 
bination with oxygen as water and is also excreted in this form. 
Oxygen is found in the free state and unites with various compounds 
of protoplasm, the process of oxidation, releasing energy. 

Nitrogen is essential to protoplasm. It forms 79 per cent of the 
atmosphere. Taken into plant bodies usually in the form of 
nitrates, the plants utilize it in the manufacture of proteins. Am- 
monia, a nitrogen compound, formed in the catabolism of plants and 
animals, is changed by certain bacteria into nitrates which are then 
absorbed by plants. 

Mineral Salts. — Proteins, carbohydrates, and fats are not the 
chief foods of man. The most important foods are mineral salts, 
water and air.^ If mineral salts are withheld from the body, death 
ensues much more quickly than from the withholding of proteins, 
carbohydrates, and fats. The salts of the body in solution aid in 
providing the proper medium for living tissues while those in com- 
bination with organic substances furnish the proper elements for 

^ Of course not all food constituents necessary to man have been evaluated. 



438 MAMMALIA— PHYSIOLOGY 

the formation of tissues. The mineral salts are necessary to main- 
tain normal physiological equilibrium and purposeful activity in the 
organism. 

Sulphur is absorbed by plants and used in the manufacture of 
some amino-acids. Phosphorus is essential to the formation of 
nuclein and lecithin of living cells. Calcium salts are necessary in 
the coagulation of blood and milk. Apparently the normal beating 
of the heart depends on the relationship of calcium to sodium and 
potassium salts. The condition known as rickets is due to a failure 
to maintain the proper ratio between the calcium and phosphates of 
the food. Cod liver oil is a cure for rickets (see page 443, Vitamin 
D). Silicon and fluorine are required in small quantities for the 
proper formation and growth of bones and teeth. They are secured 
from milk and fibrous vegetables. The ash of hair shows 40 per cent 
of silicon dioxide. Sodium as NaCl is essential to herbivorous 
animals, but the carnivores do not take salt. Raw meat protects 
the Greenland Eskimo from scurvy, rickets, and avitaminosis. 

Chlorine is important to the animal in maintaining the secretion 
of gastric juice and in keeping the optimum osmotic pressure. The 
acid-secreting cells of the stomach select for their use the NaCl of the 
blood. Potassium salts are indispensable in the synthetic processes 
of organic combination. They aid in the formation of glycogen 
from glucose, of fats from glycogen and of proteins from peptones. 
The liver, the source of glycogen, contains twice as much potassium 
as sodium. Potassium is found in red blood corpuscles and also in 
the brain and is apparently necessary to the normal function of 
organic life. Magnesium is found in greater quantity than calcium 
in the muscular tissues and the nervous system. The salts of 
magnesium aid in the formation of the albumin of the blood, reduce 
foreign matter and waste and maintain the osmotic pressure of the 
blood. Irradiation with ultra-violet light is said to decrease the 
magnesium content of rats. Magnesium requires the presence of 
calcium salts for proper function and is in fact injurious in the ab- 
sence of calcium. An excess of magnesium in the blood is said to 
cause glycosuria. Magnesium has been proved necessary for the 
growth and maintenance of white mice. The chlorophyll of green 
plants is always associated with magnesium. Copper.^ found in the 
earth in metallic form, occurs in minute quantities in most vegetable 
and animal tissues. It 7nay act as a catalyzer in the production of 
hemoglobin. 



MAMMALIA— PHYSIOLOGY 439 

lodin. — It has long been known that iodin is extremely important 
in connection with the normal functioning of the thyroid gland 
and that the latter is a powerful regulator of metabolism. It in- 
creases the rate of oxidation. Minute quantities of iodin are neces- 
sary, the human thyroid containing about one-fifteenth of a grain 
of iodin, but lack of the essential amount may cause a disease known 
as cretinism in which bodily and mental development are both 
subnormal. Iodin is an important constituent of vegetable foods 
and is found in large quantities in the plants and the animals of the 
ocean. In all probability it is in part responsible for the preserva- 
tion of the carnivorous Eskimos of Greenland. It has been suc- 
cessfully used in the treatment of pernicious anemia, given as 
thyroid extract. 

Recent discoveries would seem to indicate that the iodin-fat 
balance is important in several of the so-called vitamins, and that 
the effectiveness of cod liver oil in certain diseases is really due to 
the very small quantities of iodin present. The author of this text 
would also like to link the iodin-fat balance with his own theory 
of Fish Migration, since it is possible that the eel, fattened in fresh 
water, may need iodin to induce development of its gonads, while 
the anadramous fishes, like the salmon, possibly need to seek water 
of lower iodin content and finally to go into fresh water before their 
iodin-fat balance is reached, and eggs mature. (See page 263.) 

R. McCarrison (1919) and later the Mellanbys (1921) have 
emphasized the importance of iodin-fat balance in goiter, but until 
certain studies on the Vitamins were made (Chidester, Eaton, 
Thompson, Speicher, and others, 1928-) the significance of their 
finding was not appreciated. 

Arsenic^ found in the earth as a sulphide, occurs in minute 
amounts in animals and vegetables. Gautier and more recently 
Bertrand have emphasized the importance oi arsenic as a constituent 
of the living cell. The yolk of the hen's egg usually contains twice 
as much arsenic as the white. Arsenic enters into the composition 
of the epidermis and its appendages, the thyroid and the mammary 
glands, and the central nervous system. Arsenic resembles phos- 
phorus in its chemical affinities. It is reported that the Tyrolean 
mountain climbers habituate themselves to quite considerable doses 
of arsenic, for its energizing effects. 

Iron is an important constituent of both plants and animals. It 
Is necessary for the formation of chlorophyll In plants. Without 



440 MAMMALIA— PHYSIOLOGY 

the iron in blood, oxygen could not be carried to the tissues. Iron is 
requisite to oxidative processes and is contained in hemoglobin. 
With an ample supply of calcium^ the body needs less iron. Lack 
of iron leads to insufficient nutrition, anemia, and death. Certain 
wave-lengths of ultra-violet light increase the blood content of iron. 
Although not a constituent of the chlorophyll molecule, iron acts 
as a catalyzer in the production of chlorophyll. Millikan has said, 
" From an engineering standpoint, the universe may be said to be 
made up of the primordial positive and negative electrons, and of 
four elements built out of them; namely, helium, oxygen, silicon, 
and iron." 

Manganese. — Lindow and Peterson have presented data (1927) 
on the manganese content of eighty-four materials, covering the 
principal classes of human foods. Pineapples, beet-tops and blue- 
berries contained relatively large amounts (122-134 mgm.). Hog 
liver contained 12.2 mg. per kilogram of dry material while beef 
spleen and round steak contained none. The liver of young animals 
is the storehouse for the body's reserve of manganese and other 
mineral elements apparently necessary for the maintenance of 
physiological equilibrium. The human body contains only one- 
half ounce of manganese, but a deficiency results in disease. McCar- 
rison reports (Ind. Jour. Med. Res., vol. 14, p. 641) that daily doses 
of manganese chloride, 0.0327 mgm., caused accelerated growth in 
rats, especially marked in the males. Manganese is said to increase 
in amount as plants grow older. 

Bromine^ boron^ zinc, and aluminium are present in small quanti- 
ties in plants and are important to the life and growth of the plant. 
Their exact significance as food for the living animal is not fully 
understood. Bradley (1904) found zinc in the blood of the gastro- 
pod Sycotypus {Fulgur) canaliculatus. 

Enzymes are produced in living cells, some of which, the glands, 
are specially modified to produce important bodily secretions (pan- 
creatic juice). Enzymes are able as catalysts to hasten chemical 
reactions, but do not form a part of the end products of the reaction. 
An example of catalysis to which we have already referred (page 
436) is that of iron which in the presence of light hastens the com- 
bination of hydrogen and oxygen to form water. The genes are 
said to act as auto-catalysts in that they increase their own sub- 
stance prior to each mitosis. (See page 500.) 



MAMMALIA— PHYSIOLOGY 



441 



Nutrition and Vitamins. — Since 191 1, a great mass of literature 
has accumulated, largely consisting of the further enumeration of 
food substances characterized as belonging to groups of vitamins. 
The wholesale advertising of essential foodstuffs such as milk and 
green vegetables has resulted most favorably. A fuller appreciation 
of the virtues of cod liver oil and the tremendous importance of the 
ultra-violet and infra-red rays has also been a product of vitamin 
study. But perhaps too much time has been wasted in biological 
tests of foods long known to be chemically allied. 




Fig. 242//. Rat in advanced stage of xerophthalmia due to lack of Vitamin A. 

(Courtesy of Eli Lilly & Co.) 

Vitamin A is found in cod liver oil, butter, cream, cheese, whole 
milk, egg yolk, liver, heart and kidneys, spinach, lettuce, cabbage, 
tomatoes, carrots, sweet potatoes, parsnips, green peas, and many 
other substances. Deficiency in Vitamin A results in an anemic 
condition, with failure of ovulation and retardation of growth. The 
sense organs are diseased and pus laden, the eyes being typically 
affected by xerophthalmia with conjunctivitis and corneal degenera- 
tion. Vitamin A is fat soluble. Exposure to the air and forced 
oxygenation renders it inactive. Commercially canned tomatoes 
(no oxidation) were as rich in vitamins at the end of three years as 
fresh tomatoes. While it is generally considered that the vitamin 



442 



MAMMALIA— PHYSIOLOGY 




is completely recoverable from the unsaponifiable fraction of oils 
and fats that contain it, the writer is convinced as a result of experi- 
mentation that there are really two factors in Vitamin A, one which 
aids in curing or preventing the keratinizations characteristic of 
Vitamin A deficient animals and drawing on the stored up fats of the 
animal body, while the other, a factor belonging to the unsaturated 
hydrocarbons and fats, is the growth factor. 

It may be significant that carotin (C40H56) is an unsaturated 
hydrocarbon, and that it is transformed by the rat into Vitamin A, 

when furnished in arachis oil, 

itself unsaturated. In those 
cases where carotin and even 
chlorophyll have been able to 
induce growth in Vitamin A 
deficient rats, it is worth men- 
tioning that the experiments 
were not run long enough to 
determine the point where the 
vitamin substitute ceased draw- 
ing upon the stored up foods of 
Fig. 1±iB. Pieeon with polyneuritis , • i> 1 j ^r^i 

r„ . J- . J c • . • \j-i ■ v> the animals own body, ine 

lollowing a diet dencient in Vitamin a. ■' 

(Courtesy of Eli Lilly & Co.) writer holds that the complete 

Vitamin A contains both the 
catalyzers and the growth factor, and includes iodin, (ferrous) iron, 
and unsaturated as well as saturated fats. 

Vitamin B is found in the heart and kidneys of animals. It is 
not found in the meat of chickens, turkeys, ducks and guinea fowls. 
It is most abundantly distributed in roots and tubers and all green 
plant tissues. Cereals and the germs of seeds, yeast and wheat 
germ contain it. In man the disease known as beri-beri, with a 
failure of some nerves to function, and a disturbance of the appetite 
and digestive processes, results from eating polished rice. There is a 
resultant atrophy of the lymphoid tissue, and an hypertrophy of the 
pancreas, Spleen and certain other glands of the body. In birds a 
disease called polyneuritis is caused by similar lack of the seed coat 
in food. Vitamin B is soluble in water and alcohol. It is destroyed 
by high temperature (130° C). 

There has been so much confusion over the terminology con- 
nected with the factors contained in Vitamin B that a Committee on 
Vitamin B Nomenclature has recommended (Science, vol. 69, p. 276, 



MAMMALIA— PHYSIOLOGY 443 

1929) that the term " Bios " be used to denote the factor encourag- 
ing the rapid growth of yeast cells; that the term " B " be used to 
designate the heat labile, antineuritic factor; that the term "G" 
be used to denote the heat stable, water soluble, dietary factor called 
pellagra preventive^ which has to do with maintenance and growth. 
Alcoholic extracts of yeast lack the pellagra preventive. 

Evans and Lepkovsky showed that the glycerides of the saturated 
lauric, capric and myristic acids were beneficial to animals deprived 
of the anti-neuritic Vitamin B. In the treatment of " black-tongue " 
in dogs, which he considered the analogue of human pellagra^ Gold- 
berger had, without emphasizing its importance, added " syrup 
iodide of iron, U. S. P." to the successful diets. Perhaps Vitamin 
B may also involve the fat-iodin balance. 

Vitamin C, the anti-scorbutic, is found in lemons, oranges, 
tomatoes, cabbage, lettuce, spinach, green beans, peas and turnips. 
Oysters are rich but meat is poor in Vitamin C. Deficiency in 
Vitamin C causes a disturbance of respiratory and circulatory 
systems, loss in weight, necrosis of the teeth, with swelling of the 
gums, and the bones become friable. The disease known as scurvy 
may continue to hemorrhages and death. Infantile scurvy occurs 
in children brought up on proprietary foods. Vitamin C is soluble 
in alcohol and is destroyed by heat in the presence of oxygen, 
especially in an alkaline solution. Tomatoes, cooked in the can, 
are found to retain the Vitamin, and canned spinach is reported to 
be equal to orange juice in its Vitamin C content. 

Vitamin D controls lime and phosphorus utilization in the 
formation of bone. It was formerly included under Vitamin A. 
Egg yolks, cod liver oil and whole milk are rich in it. The mercury 
lamp and the sun are effective in activating it in the body and in 
foods. Irradiated ergosterol is an important source for experimental 
work at present. Absence of Vitamin D produces " rickets " and 
bone deformity. It is soluble in alcohol and oils. 

Excess of Vitamin D leads to an excessive precipitation of cal- 
cium in the body. An imbalance between calcium, sodium and 
potassium might be injurious, and iron assimilation might also be 
affected by excess calcium. Commercial preparations of irradiated 
ergosterol should be used only under the direction of a physician. 

Vitamin E, which prevents sterility, is found in all natural foods. 
It is especially abundant in lettuce and the germ of seeds, but is also 
found in milk and meats. It is concerned in the normal function 



444 MAMMALIA— PHYSIOLOGY 

of the placenta, and perhaps related to the metabolism of iron. It 
is not affected by ordinary temperatures. 

The writer holds that resorption of the young in female rats on a 
Vitamin E deficient diet is really an iodin effect, comparable to that 
induced in a shorter period of time by excess iodin. Wheat germ 
and hemp seed oils that are so effective in the treatment of Vitamin 
E deficiency are rich in the highly unsaturated fatty acids during 
their effective period. The effectiveness of these oils is lessened as 
the period of germination advances and the oils become more 
saturated. (See page 437.) 

What Are Vitamins? — The author holds that the " vitamins " 
are really proper combinations of minute quantities of chemicals 
that are functional as catalyzers, and make available not only the 
proteins, carbohydrates and fats that are in combination with them 
in food-stuffs, but that they also furnish the proper medium for the 
liberation of food-stuffs stored in the organism. The influence of 
these potent chemicals is felt in all glandular function, and particu- 
larly of course in the activation of the endocrine glands. 

The Organs of Internal Secretion. Endosecretory Glands with 
a Duct. Testis. — In addition to sperms, an external secretion, the 
testes furnish an internal secretion responsible for the male secondary 
sex characters. Steinach found that transplantation of the testes 
into spayed female guinea pigs induced masculinization. Lydston 
and others have transplanted human testes, with temporary benefit.^ 

Ovary. — The ovary produces eggs and regulates the female 
secondary sex characters. In the fowl Goodale found that removal 
of the ovary causes the bird to take on male plumage. Domm found 
that a compensatory testis-like structure developed on the right side. 
Steinach found that castrated male guinea pigs could be feminized, 
by implanting ovaries in their body cavities. 

In early or normal menopause, and in epilepsy, ovarian extracts, 
notably corpus luteum and folliculin extract, are beneficial. Allen 
and Doisy have cured some cases of sterility with follicular liquid. 

Liver. — The liver secretes bile externally, and produces glycogen^ 
a " negative internal secretion " which is an important body food, 
and transforms harmful ammonia into harmless urea. A hormone 
extracted from liver has been most successful in the treatment of 
pernicious anemia. 

^ Consult Moore, C. R. 1926. Qu. Rev. of Biol., vol. i, pp. 4-50. 



MAMMALIA— PHYSIOLOGY 445 

Pancreas. — The digestive enzymes of the pancreas act on pro- 
teins, carbohydrates and fats. The internal secretion,(^£^£r£^^ 
successfully isolated by Banting^ and associates in 1922, was secured 
from the Islands of Langerhans of the pancreas of fetal calves. 
J. J. Abel has since then prepared pure crystalline i nsulin, so power- 
ful that only i/ioo of a grain is the daily dosage for a diabetic. 
Many lives are now saved annually by the use of " insulin." 

Endosecretory Glands without a Duct. Thyroid. — The thyroid 
glands contain ten times as much iodin as any other organ in the 
body. Iodin in food and water must be optimum, or goiter may 
result. The thyroids stimulate carbohydrate and calcium metab- 
olism and bear an important relation to body fats. Pioneer studies 
by Gudernatsch with tadpoles indicated that if fed thyroid extract, 
they metamorphosed rapidly into small toads. Uhlenhuth has 
shown that anterior lobe substance from the pituitary gland will 
stimulate the thyroid and induces precocious metamorphosis in 
amphibia. In hypersecretion of the thyroids, goiter or exophthalmic 
goiter may result. In the latter, the eyeballs protrude and the pulse 
is greatly accelerated. Hyposecretion results in colloid goiter, cretin- 
ism, or myxedema. Cretins are dwarfed, with low mentality, and 
are frequently deaf mutes. Myxedema (mucous fat) is accompanied 
by great increase in weight, retarded bone growth, brittle teeth, 
slow pulse, thickened, wrinkled skin and slow metabolism. Thy- 
roxin (Kendall) and thyroid extract have been used in the treatment 
of cretinism, myxedema, and endemic goiter. It is dangerous to 
start to furnish a community additional iodin in drinking water, 
as some goitrous persons may be injured. But the campaign of 
education about the importance of sufficient iodin in food and water 
(McClendon, Minnesota; and the South Carolina Board of Health) 
is admirable. 

Applying the discoveries of Bloor, Hill, Sperry and others that 
under certain intestinal conditions iodin may be discharged from the 
body in considerable quantities in \\iQ feces, Chidester has suggested 
that in the cases of water-borne goiter recorded by McCarrison and 
others, it is quite likely that certain bacteria will cause the liberation 
of iodin and that subsequent demands made on the thyroid by the 
excess of unsaturated fatty acids in the intestine will cause thyroid 

1 But Banting and Best in the Journal of Laboratory and Clinical Medicine, 
1922, Vol. 7, p. 467, gave full credit to E. L. Scott for his pioneer studies, described 
in 19 1 2 in the American Journal of Physiology, Vol. 29, p. 306. 



446 



MAMMALIA— PHYSIOLOGY 



hypertrophy. Possibly disturbance of the calcium-iodin balance 
will also account for non-bacterial cases due to water. 

The writer cannot resist the opportunity to again pay tribute to 
McCarrison for his initial discovery of the significance of the iodin- 
fat balance and to deplore the fact that it is now receiving such 
belated recognition, more than twelve years after its discovery, 
in 1919. 



Internal Jugular vein j-r^K " 

Middle thyroid vein — 
Inferior thyroid vein-—. 



Thyroid 

— Common carotid 




Median furrovi/ 
of thymus 



Lun^- 



FiG. 243. The thyroid and thymus in a child of six months. (Sappey.) (Schafer's 
Text Book of Mic. Anat. Courtesy of Longmans, Green & Co., London.) 

Parathyroids. — The parathyroids have been operatively removed 
with the thyroids, and death ensued, after a condition of tetany. 
The parathyroids influence calcium metabolism, and also affect 
sugar metabolism, and aid in preserving the nitrogen balance. 

Thymus. — The thymus gland degenerates at puberty, and may 
be concerned with both the thyroids and the gonads. Soli, and 
later. Riddle, believed that the thymus was concerned with calcium 



MAMMALIA— PHYSIOLOGY . 447 

metabolism and shell formation in the birds. Crew reported (1928) 
that removal of the thymus had no effect on calcium metabolism 
in fowls. 

Snp7'arenals. — It has long been known that the suprarenal 
glands are essential to life. The suprarenal medulla is the source 
of epinephrin (adrenalin) which was the first hormone to be isolated 
chemically (Takamine) and is extremely potent, one part in eight 
billion producing reaction in the rabbit intestine. Wheeler and 
Vincent found that as long as an adequate amount of cortex sur- 
vived, destruction of all of the medullary tissue led to no ill effects. 
Addison's disease is caused by pathological changes in the cortex 
and is characterized by reduced blood sugar, subnormal temperature 
and a peculiar pigmentation of the skin, with muscular weakness. 

In October, 1927, Rogoff and Stewart described the results 
obtained with 0.9 per cent NaCl or glycerol extract of the cortex. 
They treated completely adrenalectomized dogs. Of thirty dogs 
treated, six lived longer than the longest of the control animals. 
They did not give the average survival of treated animals as com- 
pared with controls, which should have been done. In the same 
month, 1927, Hartman, MacArthur and Hartman described the 
first method for preparing an epinephrin-free extract of the adrenal 
cortex. By the use of such an extract, the average survival period 
of completely adrenalectomized cats was markedly increased (21 
days) over that of controls (6 days). This average included all 
cats treated, even those complicated by infections. 

In March, 1930, Swingle and Pfiffner described a method of 
preparing a concentrated extract of the adrenal cortex sufficiently 
potent to maintain the lives of adrenalectomized cats indefinitely. 
Their process was very complicated and their extract contained 
much epinephrin and inert material. In June, 1930, Hartman and 
Brownell described a much simpler method of preparing a concen- 
trated extract of the adrenal cortex containing less than i : 100,000 
epinephrin. With this extract it is possible to maintain the lives 
of adrenalectomized cats indefinitely. One animal was kept alive 
for 268 days, dying because the extract was discontinued. This 
substance, found in the adrenal cortex, which is essential to life, 
has been called cortin. Both Swingle and Hartman have furnished 
extracts to clinicians who have successfully treated cases of Addi- 
son's disease with them. 

Suprarenal virilism is found in some women with diseased 



448 . MAMMALIA— PHYSIOLOGY 

adrenals. Cannon ^ demonstrated the effect of increased suprarenal 
activity on blood sugar, muscular activity, and recovery from 
fatigue. Fear or anger enables one to fight better or run faster! 

Pineal Body {Epiphysis). — In cases of pineal tumor, causing 
deficient secretion, there is a tendency to obesity and individuals 
may be sexually precocious with premature ossification of the bones. 
Pineal extract has been administered to cases of retarded mental 
development, with reports of gratifying improvement. But we 
really know very little about pineal function. 

Pituitary Body {Hypophysis). — The pituitary has two lobes, an 
anterior one and a posterior one, each with distinct functions. In 
cases of hypersecretion of the anterior lobe., acromegaly and gigantism 
may result. The hair is excessive, teeth are widely separated, the 
extremities are elongated and the fingers become broad and spade- 
like. The skin is thick and wrinkled and the sweat and sebaceous 
glands are excessively active. Glycosuria and excessive gonadial 
development may also occur. The stimulating influence of anterior 
lobe substance on the thyroids has already been noted (p. 445)- 

P. E. Smith and E. T. Engle (Am. Jour, of Anat., vol. 40, pp. 
159-217, 1927) have shown that the implantation of anterior 
hypophyseal substance in infantile female rats and mice will induce 
sudden and extensive ripening of the Graafian follicles. After 3 
days of implantation they induced the ripening of 48 ova in a 22- 
day mouse. There is correlation between the sizes of rabbits and 
the number of young. Larger breeds are thus affected in growth and 
ovulation by the anterior hypophysis. Hyposecretion of the anterior 
lobe results in infantilism, obesity, a thin, smooth, dry skin, scanty 
hair, slender fingers, and dwarfism with the torso longer than the 
extremities. The oxidative metabolism is low. 

Hypersecretion of the posterior lobe causes contraction of the 
smooth muscles, resulting in a rise in blood pressure. Pituitrin 
is used in obstetrics since it keeps smooth muscle contracted longer 
than does adrenalin. Sugar tolerance is decreased in hypersecretion 
of the posterior lobe. Hyposecretion of the postej'ior lobe results in 
subnormal temperature, increased sugar tolerance and adiposity 
accompanied by drowsiness (Dickens' fat boy). Epilepsy fre- 
quently occurs. 

^ Consult Cannon, " Bodily Changes in Pain, Hunger, Fear and Rage." 



MAMMALIA— PHYSIOLOGY 449 

Dr. Oliver Kamm reported^ (December, 1928) the isolation of 
two hormones from the posterior lobe of the pituitary. The alpha 
hormone is effective in obstetrics, contracting the uterus, while the 
beta hormone raises blood pressure and also controls the excessive 
output of water and its utilization in the body tissues. Fleshy 
people (the physiological wets) are extremely sensitive to the 
action of the beta hormone, while slender scrawny ones (the physio- 
logical drys) quickly return to normal after the administration of 
this hormone. Both hormones act immediately to increase the 
sugar of the body and thus offset an overdose of insulin. 

References on the Endocrines 

Barker, L. F. 1925. Endocrinology and Metabolism. D. Appleton 

and Co. 
Cooper, E. R. A. 1925. The Histology of the More Important Human 

Endocrine Organs at Various Ages. Oxford University Press. 
DoDDS, E. C, AND Dickens, M. A. 1925. The Chemical and Phys- 
iological Properties of the Internal Secretions. Oxford University 

Press. 
Falta, Wilhelm, and Meyers, M. K. 1923. Endocrine Diseases. 

P. Blakiston's Son and Co. 
Sharpey-Schafer, E. The Endocrine Organs. Part I, 1924, and Part 

II, 1926. Longmans, Green and Co., Ltd. 
Vincent, Swale. 1925. Internal Secretion and the Ductless Glands. 

Physicians and Surgeons Book Co. 

The Circulatory System. — The blood vessels are a system of tubes 
completely closed except where the lymphatics open. In one place 
the system is dilated into a large complexly formed rhythmically 
contractile organ, the heart, which is the central portion of the 
circulatory system and, according to the studies of O. C. Glaser 
(193 1), works basally against the resistance offered by the system 
of enclosed tubes. According to the author, objections may be 
offered to this view because of its apparent simplicity which does 
not seem to take account of the numerous influences which may 
temporarily modify the tubal resistance. There are several kinds of 
channels in which blood flows: (i) Vessels taking blood from the 
heart — arteries. (2) Vessels taking blood to the heart — veins. (3) 

2 Kamm, O. Science, vol. 67, p. 199, 1928; J. Am. Ch. Soc, vol. 50, p. 573; 
Science, vol. 69, p. 85, 1929. 



450 



MAMMALIA— PHYSIOLOGY 




^^xfernol maxillary 

/Posterior auricular 
Liricjuo/ 

Musculan's 
Thyroid 

Thyrocervicol 
Brachial 
Left carotid 
Vertebral 
Costocer vicol 
/nternal mammary 
M&dio^tinal 
Left subclai^ian 
Ihhominate 

Ductus botalli 
Pulmonary 
Brorichiol 
Ttiorocic aorta 

■Coronary 
Heart 



Intercosto/ 

■T- Oostr/ca sinistra 

Hepatic 

Coe/ioc 

Superior mesenteric 
-Abdominal aorta 
-/^brenic 

— Ad re no- /umbolis 
Suprarenal gland 

Reno/ 

— Kidney ^ ^ „ 

— Ovarian (or spermatic) 
Lumbar 

■Inferior mesenteric 

//ioiombal/s 

-External iliac 

-Caudal 

-Internal Iliac or tiypo<jastric 

-Epigastric 

.t^emoral 

■Deep femoral 



Fig. 244. Arteries of the cat. (Drawn by W. J. Moore.) 



MAMMALIA— PHYSIOLOGY 



451 




jrrS; 



Anterior' foc'iot 

Trons\/erse 
Posferior fac/al 
fnterno/ Ju<]Ular 
Inferior thyroid 

Supra - scopti/or 



3ubclov/an 



- Costocervicot 
Verfebral 
Inferno/ mammary 



Precavat 

Azygos 

Intercosfal 
Coronary 



Postcaval 



Phrenic 



Hepatic 

Veins of liver 
Portal 

A drenolumbalis 

Renal 

0\/orion (or spermatic) 

Lumbar 

I/iolumbo//3 



Common iliac 

Caudal 

fnterno/ iliac or hypogastric 

Epigastric 

Femoral 

Deep femoral 



Fig. 245. Veins of the cat. (Drawn by W. J. Moore.) 



452 



MAMMALIA— PHYSIOLOGY 



Vessels conveying blood to tissues and intervening between arteries 
and veins — capillaries.^ 

The heart is a thick, muscular, hollow organ with great blood 
vessels originating from the broad anterior part. It is enclosed in a 
sac of fibrous tissue lined with epithelium called the pericardium. 
It consists of 4 chambers, 2 of which are called auricles and 2 
ventricles. 

The auricle and ventricle of the right side are completely sepa- 
rated from those of the left side. The auricles open into the ven- 
tricles by valved apertures and valves guard the openings of the 
great vessels. Between the right auricle and right ventricle is the 
tricuspid valve. Between the left auricle and the left ventricle is the 
mitral or bicuspid valve. Between the auricles is a partition (auricu- 
lar septum). Between the ventricles is the ventricular septum. 




X i6oo X 750 

Fig. 245^. Red and White Corpuscles of Human (Left) and Frog (Right) Blood. 

* (Drawn by Norris Jones.) 



There are two large veins which empty into the right auricle. 
The superior vena cava descends, while the inferior vena cava ascends. 
The coronary veins come from the heart substance itself. Into the 
left auricle, four pulmonary veins enter, two coming from the right 
and two from the left lung. 

From the right ventricle arises the large pulmonary artery 
which divides into a branch for each lung. From the left ventricle 

^ In the portal system (page 453) the capillaries in the liver intervene between the 
hepatic portal vein and the hepatic veins. 



MAMMALIA— PHYSIOLOGY 



453 



the large aorta originates. These arteries are guarded by semi-lunar 
valves which consist of three pouches with the convex side towards 
the ventricle. 

Action of the Heart. — The right ventricle pumps blood through 
the lungs, while the left ventricle forces it through the rest of the 
body. Closely following the contraction of the auricles is the con- 



Poncreotico-_ 
duodenal vein 

Doodenurn ■ 



Pancreas 




Post cayal vein 



Phrenic vein 

— Oo 5 fro- epiploic vein 



— Coronary vein 
— Portal \^ein 

-Dorsal surface 
of stomacft 

-Oosfro- splenic vein 



Anterior mesenteric vein 



Posterior mesenteric vein 



Spleen 



Fig. 246. Portal system of the cat. (Drawn by W. J. Moore, after I. M. Wilder, 

Anat. Rec, 191 9.) / 

traction of the ventricles and in this case the thick-walled left 
ventricle contracts with more force than the right. Contraction 
is termed systole. Relaxation is termed diastole. Besides systole 
and diastole there is a short passive period in which there is neither 
contraction or relaxation. 

Pulse. — In men the average frequency of the pulse is from 60 to 
70, while in women it varies from 65 to 80 beats per minute. There 



454 MAMMALIA— PHYSIOLOGY 

is a quite definite correlation between longevity and the rapidity 
of the pulse. (See tables, pages 496 and 498.) 

Portal Circulation. — The blood which comes to the spleen, 
stomach and intestines passes first through the capillaries of these 
organs and then by their veins into one, the portal vein, which goes 
to the liver and there breaks up into capillaries, then passes from 
the liver into the post cava. The wastes are conveyed from the 
liver by way of the bile duct which leads into the digestive tube. 
But bile acids and salts are extremely important. 

The Comparative Anatomy of the Portal Systems. — In a portal 
system the blood is collected in capillaries, passes through a vein to 
an organ of purification, thence by capillaries to another vein that 
brings the purified blood into the heart. 

(i) The hepatic portal system consists of the union of veins from 
the stomach, intestine, spleen and pancreas, which passes into 
the liver as the hepatic portal vein, then breaks up into capillaries, 
its blood mingling with the blood brought into the liver by the 
hepatic artery. Capillaries in the liver unite to form the hepatic 
veins which send the purified blood into the sinus venosus. The 
hepatic portal system persists throughout the vertebrates. 

(2) The rey^al portal system arises in the Elasmobranchii and 
almost completely disappears in the Aves. 

Elasmobranchii. The caudal divides into right and left portal veins which pass to the 
kidneys. The course thence is to the cardinal veins. 

Teleostii. The caudal divides into two branches, of which the right continues 

into the corresponding cardinal and the left breaks up in the kid- 
ney. 

Amphibia. Salamander. 

The caudal divides into two renal portal veins. The efferent renal 

veins form the postcaval. 
Frog. 

The femorals each divide into a dorsal and a ventral branch. The 
ventral branch, the pelvic vein, unites with its fellow to form the 
abdominal vein. The dorsal branch becomes the renal portal, 
receives the sciatic and passes to the kidney. 

Reptilia. The turtle has no renal portal system. In the lizard the caudal 

divides into two pelvics which become the renal portals. As in 
the salamanders, the efferent renal veins unite to aid in forming 
the postcaval. 



MAMMALIA— PHYSIOLOGY 455 

Aves. In the birds the renal portal system has almost completely disap- 

peared. The two renal portal veins formed by the division of the 
caudal send off only a few branches to the kidneys, known as the 
efferent renal veins, the main vein passing through the substance 
of the kidney and joining the femoral vein from the leg to form the 
iliac vein. The two iliacs unite to form the postcaval. 

Mammalia. There is no trace of a renal portal system in the mammalia. 

Blood. Functions of the Blood. — i. Carries food-stufFs to the 
tissues. 

1. Carries oxygen to the tissues. 

3. Medium of transmission of the internal secretion of certain 
glands. 

4. Removes waste products from the tissues and carries them to 
the organs. 

5. Aids in equalizing the temperature and water content of the 
body. 

Amount of Blood in Per Cent in Different Parts of the Body 

Spleen 0.23 per ce 

Spinal cord and Brain 1.24 pe/cent 

Kidney 1.63 nfer cent 

Skin 2.10 ier cent 

Intestines 6.30 peTiBent 

Bones 8.24 per oent 

Heart, Lungs and Blood vessels 22.76 peyxent 

Resting muscle 29.20 p/r cent 

Liver 29.30 |(gr cent 

Chemical Composition of the Blood. (Schmidt) 

Water 788.71 pe/cent 

Proteins and extractives 191.78 pM^xent 

Fibrin (from fibrinogen) 3.93 per cJnt 

Hematin (and iron) 7.70 pec/cent 

Salts 7.88 per cent 



1,000.00 peVsent 

Blood constitutes about 7 per cent by weight of the human body, 
a man having about 5 liters of blood in his body. Its specific 
gravity varies from 1,050 to 1,055 ^^ children and women, and from 
1,057 to 1,062 in men. The specific gravity of the corpuscles is 
about 1,105, and that of the plasma, about 1,030. The specific 
gravity is generally in direct proportion to the hemoglobin percentage 




456 MAMMALIA— PHYSIOLOGY 

and the volume of (red) corpuscles. According to Schmaltz, blood 
with a specific gravity of 1,059 has 100 per cent of hemoglobin, that 
with a specific gravity of 10,575 has 90 per cent hemoglobin, while 
blood with a specific gravity of 1,049 ^^^^ have a hemoglobin content 
of but 60 per cent. 

Blood has an alkaline reaction; this is at a maximum after meals 
as the acid gastric juice is then in the stomach. The alkalinity is at 
a minimum after exercise because of the HCO2 formed by contrac- 
tion of the muscles. Blood has a salt taste and a faint smell. 
Coagulation of blood is promoted by heat and standing, and re- 
tarded by cold and the salts, sodium phosphate, sodium citrate and 
magnesium phosphate. 

Blood consists of erythrocytes (red corpuscles), leucocytes 
(white corpuscles), platelets, hematokonia or blood dust. Salt 
solution swells the corpuscles and pure water will dissolve out 
hematin from the red ones. Water has no action on the white 
ones. We consider the red blood corpuscles as dead and the white 
ones as very much alive. 

"Thrombocytes, usually spindle shaped, occasionally spherical, 
are found in all of the vertebrates except mammals, in which only 
thromboplastids (minute, cytoplasmic platelets) are found. Both 
thrombocytes and platelets are associated with the clotting of the 
blood. Lymphocytes are uniformly present in all classes of verte- 
brates. Monocytes or, large mononuclear leucocytes, are also 
uniformly present in all vertebrates. In man the neutrophilic leu- 
cocytes predominate numerically." (A. B. Dawson.) 

The proportion of white to red corpuscles is as i : 300 or as 
I : 500. There are many more white corpuscles shortly after meals. 
The reds vary in number as one goes from sea level to the mountains. 

Size of reds Number of reds 

Animal in microns in i cubic mm. 

Elephant 9. 

Man '].i-i.^ 5,000,000 

Monkey 7.0 6,355,000 

Guinea Pig 7.48 5,859,000 

Dog 7.2 6,750,000 

Horse 5.58 7,403,000 

Cat 6.2 9,900,000 

Spanish Goat 4.25 19,000,000 

Napu Deer 2.0 

(From RoUett and Bethe in Bohm-DavidofF-Huber's Histology, W. B. Saunders Co.) 



MAMMALIA— PHYSIOLOGY 457 

Red corpuscles or erythrocytes consist of water, hemoglobin, 
nucleoproteid, lecithin, cholesterin and salts of potassium and of 
phosphoric acid. The erythrocytes of fishes, amphibia, reptiles and 
birds are oval and nucleated and the leucocytes are frequently 
found to be without nuclei. The erythrocytes are biconcave discs 
in all mammals except the Camelidae in which they are oval^ but in 
healthy animals, non-nucleated in adults as in other mammals.^ 
Sometimes in man after anemia or severe hemorrhage, nucleated 
reds are called forth from the red bone marrow where they are 
formed in adults. In the embryo, the liver and the spleen produce 
nucleated reds, but in the adult the spleen devours worn out reds 
and furnishes some lymphocytes. The spleen probably takes some 
of the iron from worn out red blood corpuscles while the liver takes 
iron and uses hemoglobin in forming bile-pigment, bilirubin. The 
thymus, tonsils and other lymphoid glands supply leucocytes, 
acting as foci of multiplication for the cells which originate as 
myelocytes in the bone marrow. 

When blood is treated with Os04 it shows colorless, round disks, 
which are unstable, and also granules. The disks are " thrombo- 
plastids" or blood platelets.'^ The proportion of red corpuscles to 
platelets is as 80 : i or as 20 : i. They are foci where coagulation 
of the blood is hastened. F. F. Lucas has photographed blood 
platelets with ultra-violet light and discovered that they have 
." naked, sticky surfaces " such that they are able to glue themselves 
together with available blood corpuscles and facilitate rapid blood 
clotting. Howell believes that platelets are more than mechanical 
agents in causing coagulation of blood and lymph. 

Blood Groups. — In blood transfusions, it is necessary that the 
blood of the donor and the recipient be alike, and that the substance 
known as a hemolysin be absent. In hemolysis, a substance is 
produced which has the power of dissolving the introduced red 
corpuscles. Hemolysis does not occur without agglutination 
(clumping) (see page 458) and it is therefore only necessary to test 

* Since two texts of recent date have published the erroneous statement that Cam- 
elidae have nucleated erythrocytes, the question was referred to Dr. W. H. F. Addison 
and to Dr. Noback, both of whom reported that they are oval, biconvex and non- 
nucleated. A paper by Ponder, Yeager and Charipper, Haematology of the Camelidae, 
Zoologica, vol. ii, no. i, Dec. 5, 1928, furnishes additional proof. 

* Corson, Irwin and Phillips found (1930) that irradiated ergosterol (Vitamin D) 
increased the number of thrombocytes in the blood of rats, and materially shortened 
the time of coagulation. Blood calcium was increased. 



458 MAMMALIA— PHYSIOLOGY 

for the agglutinins, before utilizing the blood of a donor. In 1901, 
Landsteiner showed that human beings may be divided into three 
groups according to the interactions of their sera and blood cells. 
Later his pupils, Decastello and Sturli, added a fourth group. 
Blood from two persons of the same group will mix freely, but the 
blood from two different groups will clump or agglutinate. 



Inagglutinable; contain no agglutino- 
gen. 

Agglutinated by serum of groups O and 
B; contain agglutinogen A. 

Agglutinated by serum of groups O and 



Landsteiner's Table of the Constitution of the Four Blood Groups 
Group Serum Cells 

O Agglutinates cells of three other groups; 

contains agglutinins alpha and beta. 
A Agglutinates cells of groups B and AB; 

contains agglutinin. 
B Agglutinates cells of groups A and AB; 

contains agglutinin. A; contain agglutinogen B. 

AB No agglutinative effect; contains no ag- Agglutinated by serum of groups O, A, 

glutinin. and B; contain both agglutinogens A 

and B. 

Moss's classification of blood groups has to some extent replaced 
the earlier ones of Landsteiner and Janksy. Hooker and Boyd 
of the Evans Memorial Hospital, Boston, have studied (1929) the 
chances of establishing a child's paternity by blood grouping tests. 
A child's blood may belong to the same or a different blood group 
from its mother. Some investigators believe that the characteristics 
follow the Mendelian Law and may be inherited from the grand- 
parents.^ 

Lyinph. — Except for those red corpuscles accidentally present 
in it, lymph may be considered to be blood minus the erythrocytes. 
Lymph bathes every cell and tissue of the body, and mediates inter- 
changes between the tissues and circulating blood. It has several 
important functions: (i) The conveyance of food and of oxygen 
inward from the capillaries to the cells and the external transporta- 
tion of the tissues' waste. (2) The absorption of fat from the diges- 
tive tube. (3) The lubrication of great serous surfaces. (4) The 
upkeep of fluids in the brain and spinal cord. (5) The maintenance 

^ Consult K. Landsteiner, The Human Blood Groups, pp. 892-908; R. Ottenberg 
and D. Beres, The Heredity of the Blood Groups, pp. 909-920; in Jordan, E. O., and 
Falk, I. S., The Newer Knowledge of Bacteriology and Immunology, U. of C. Press, 
1928; and the summary by L. H. Snyder, Arch. Path, and Lab. Meth., vol. 4, pp. 215- 
257, 1927. 



MAMMALIA— PHYSIOLOGY 



459 



S -Thoracic c/uct 



of the optimum composition of the blood, even at the expense of the 
constancy of lymph. 

Lymph consists of nutritive material absorbed from the walls of 
the alimentary canal and colorless food materials in the blood not 
yet utilized. After meals the color of lymph becomes whitish from 
the admixture of chyle^ and 
many fat droplets are pre- ^' 

sent. Lymph coagulates 
when drawn, since the fibrin 
factors are present; but the 
process is less prompt and 
the clot is less firm than in 
the case of blood. Lymph 
contains three proteins, 
fibrin, serum-globulin, and 
serum-albumen. It con- 
tains, in common with 
plasma, cholesterin, sugar 
and inorganic salts. The 
proteins are less abundant 
than in plasma. The 
amount of urea is greater 
than in plasma. 

Lymphatics. — From the 
alimentary canal, materials 
pass in part directly into 
the blood vessels surround- 
ing the canal, and in part 

into vessels called lacteah 

1 • 1 r J • ^u '^^ Fig. 247. Diagram of paths of absorbed 

which are found m the mtes- ^ , 1 ^' , ° ■ ^ ,t^ n 

, .... _ , food from the digestive tract, (trom Lonn 

tmal villi. Lacteals trans- ^^^ Budington. Courtesy of Silver, Burdett 
port chyle to the receptac- and Co., New York.) 
ulum chyli of the thoracic 

duct. The lymphatics and the lacteals form a simple, branched 
vascular tree which opens into the jugular veins at their bases by two 
trunks, the left-thoracic duct and right-lymphatic duct. Through- 
out the course of the lymphatic vessels are many lymphatic glands 
which are the foci of multiplication of white blood corpuscles and 
act as strainers for poisons. (Figure 246.) 

Flow of Lymph. — No organ corresponding to the heart keeps the 



( V h 


^- 


% 










Y 


it/ 


■••to 

ft 








\ 


* 


H 






X 


B 


\ ■ 








/ 


fln 


p<..— . 


-] — From 
r:~Lactea 


Sti 


ornoc/i 


Portal vein ^ 
From spleen' 


% 




'Is- 


or 


A 




M- 


; /ymph 


^esse/s 



460 MAMMALIA— PHYSIOLOGY 

lymph current in motion. The main cause for its direction from the 
extra-vascular spaces toward the veins in the neck is the degree of 
pressure to which it is subjected in those spaces as compared with 
the small pressure near the ends of the great ducts. Lymph flow 
somewhat resembles that of venous blood, but is less regular and 
more sluggish, though not so slow as might be supposed. 

S-pleen. — While the mammalian spleen may be operatively re- 
moved, it serves several important functions: (i) During embryonic 
life and even after birth, in cases of anemia, the spleen forms red 
corpuscles. (2) It contains large quantities of organic iron and 
probably aids in the preparation of hemoglobin. (3) It destroys 
old worn-out red corpuscles and takes up pigment and other wastes 
from the blood. (4) It increases in size during digestion and after 
the fifth hour slowly decreases to normal size. It is excessively 
vascular during digestion. 

Respiratory System. — In the cat the respiratory system is not 
greatly different from that of man. Air inhaled at the anterior 
nares goes through the nasal passages and out from the posterior 
nares into the naso-pharynx, Lucas ^ finds that in the monkey the 
cilia of the septum, the middle concha {turbinate) , and the middle 
meatus sweep the mucus downward toward the floor and hence 
backward into the naso-pharynx (not upward as senior authors have 
claimed). The trachea of the cat consists of forty-five cartilages 
(16-20 in man) which are held in place by fibrous membrane which 
embeds them. In the cat the trachea is three-fourths of an inch in 
diameter and four and one-half inches in length. The lungs consist 
of three lobes on each side with a fourth lobe on the right side which 
is divided into two parts, and lies a little to the right of the middle of 
the body. The cartilaginous rings extend two-thirds of the way 
around the trachea, the third not supported by the rings resting 
upon the esophagus. The lungs are supported in the chest by paired 
bronchi and the pulmonary and bronchial arteries, veins and 
lymphatics. The bj-onchi also have incomplete irregularly arranged 
cartilaginous rings. Each lung is covered by a delicate serous 
membrane, the pleura^ which is reflected over the inner surface of 
the thorax. The lung consists of many lobules of air-cells with 
extremely thin walls and is richly supplied with minute capillaries 
as well as many veins and arteries. In the trachea and the bronchi, 

* Lucas, A. M., in Chapter 1 1 of Special Cytology, 2d edition, edited by E. V. 
Cowdry, 1931. 



MAMMALIA— PHYSIOLOGY 



461 



the ciliary movement is upward towards the throat. Inhalation of 
chloroform stops ciliary activity, while ether does not (Lucas). 
Hach found (1925) that morphine slowed the rate of movement 
of pollen injected into the trachea of dogs, but that caffein increased 
the speed of its transportation. 

Respiration. — During the first year of life, the average rate of 
respiration in the human infant is about forty-four per minute. 
It gradually reduces to a rate of about fourteen or fifteen per minute 
in the adult. 



Table of Respiration Rates of Various Animals. (Bert ^) 

Hippopotamus i per minute 

Lion 

Horse 

Pig 

Ox 

Dog 

Sheep and goat i 

Cat 24 

Pigeon 30 

Eel 50 

Rabbit 55 

Sparrow 90 

Rat (asleep) 100 



I 






10 






10 


to 


12 


10 


(< 


!<; 


15 


<( 


18 


I^ 


<( 


20 


18 


(( 


20 



« 
« 
« 

« 



How Long Can Aquatic Mammals Submerge'^ — It is well known 
that by practice it is possible for man to remain submerged for over 
two minutes (see page 157). Parker, in some recent observations, 
has shown that the Florida manatee can remain submerged sixteen 
minutes. The whale, reported to submerge for an hour, has been 
found by Parker to remain twenty minutes under water. 

Voices of Mammals. — In man, the dog, the sheep, and the horse, 
the voice is produced by expiratory blasts of the lungs producing 
vibrations of the vocal cords. The pitch of sound and tones depends 
on the tension of the vocal cords, a low-pitched tone being produced 
by relaxed cords. In the cat, the pig and cattle, the voice is an 
inspiratory act. The whale, the dolphin, and the giraffe are mute. 

The Excretory System. — The urinary system of the mammal 
consists of paired kidneys where solid products of decay that cannot 
be eliminated by the lungs are excreted in the urine which passes 
from the kidneys by way of the ureters to the ventrally situated 

^ Dearborn, G. V. N. 1908. Human Physiology. Lea and Febiger, Philadelphia. 



462 



MAMMALIA— PHYSIOLOGY 



urinary bladder. From thence it is transported by means of the 
urethra to the exterior. The kidneys expel water, urea and a little 
CO2. The average amount of urine secreted in man per day is 
fifty ounces. The lungs exhale CO2 and water with a trace of urea, 
while the skin excretes as the lungs do and also functions in place of 
the kidneys when they are diseased (see Perspiration, page 428). 
The liver, by means of its hepatic portal system (see page 454), 
separates out the impurities from the blood and passes them into 
the duodenum. Intestinal excretion plays an important role in the 
economy of the animal. 




Fig. 248. Graafian follicle and ovum of the cat, within the ovary. (Photograph 
through the courtesy of Dr. B. F. Kingsbury.) 



Reproductive System. — While in the lower vertebrates there is 
an extremely close relationship between the urinary and the repro- 
ductive system, evidenced in the frog, for instance, by the passage 
of sperms through the kidney and out through the common Leydig's 
duct, we find that in the mammal, at birth, such connection largely 
disappears. 

Female. — In the cat there are two small oval ovaries^ which 
produce Graafian follicles and send the ova therein contained down 
the elongated Fallopian tubes, the lower portions of which, as horns 



MAMMALIA— PHYSIOLOGY 



463 



Protoplaamic 
eiop 



(cornua) of the bicornuate uterus^ retain the embryos until they 
have matured. The body of the uterus in the cat does not receive 
the implanted ovum. Subsequent to the extrusion of the ovum, the 
follicular epithelium of a Graafian follicle degenerates, collecting in a 
mass of cells of a yellowish color called the corpus luteum (see p. 444). 
In higher mammals (cow, man) the Fallopian tubes or oviducts 
function merely to convey sperm and to carry the eggs to the body 
of the uterus. Parker finds that, in reptiles and birds, a proovarian 
tract of cilia conducts the sperms upward, and an extensive ab- 
ovarian tract propels the ova downward. Parker has recently 
(1931) shown that in the rabbit muscular contractions and ciliary 
activity together move the sperms upward and the ova downward. 
The eflPective stroke of all cilia is toward the uterus. The Fallopian 
tubes and the uterus are suspended by the broad ligament attached 
to the dorsal abdominal wall. 

The delicate round ligament \ ^Acmome 

also aids in the suspension of Head ■! M Nucleus 

these structures. The body of 
the uterus continues posteriorly 
to form the vagina. From the 
urinary bladder leads the female tliddlePiSce 
urethra which ends in the cat at 
the vestibule, about one-half inch 
from the external opening of 
the vagina, the vulva. On the 
ventral surface, just posterior to 
the opening of the urethra, ap- 
pears the clitoris, which is the ji^uvPiece • 
homologue of the penis of the 
male. Bartholin's glands are 
situated lateral to the vestibule 
with ducts opening into it. The 
vagina, uterus, and the Fallopian 
tubes are all lined with mucous 
membrane richly supplied with 
glands. EndPiece 

Male. — The paired testes of 

the cat consist of numerous min- ^^^ ^^^^ Diagram of animal sperm 
Ute coiled tubules, the seminifer- as in mammals. (After Wilson, The Cell. 
OUS tubules, which in each testis Courtesy of The Macmillan Company.) 



Head 

Neck 

Connecting or 



— Envelope 

; Proxinval CentnoU(c9 

, '"dSmi CentHole i^ 



^ial rvlament 

Tall Envelope 



464 



MAMMALIA— PHYSIOLOGY 



unite into a few beneath the elongated epididymis which continues to 
form the vas deferens. These canals transport the spermatozoa to 
the urethra. By the activity of the ciliated epithelial cells lining the 
efferent ducts, the then immotile spermatozoa are slowly passed 
toward the epididymis. The penis, by means of which sperms are 
transferred, receives the urethra. The prostate glands surround 
the urethra dorsolaterally a short distance from the urinary bladder. 
They secrete a fluid which serves as a medium for the spermatozoa. 
The spermatozoan has a long flagellum, and its activity is affected 

by changes (CO2, acidity) in 
the seminal fluid, just as the 
beat of the cilia may also be 
affected. Cowper's glands are 
situated posterior to the pro- 
state glands and secrete a vis- 
cid fluid which passes into the 
urethra by a duct from each 
gland. 

Propagation Rate in Mam- 
mals. — In the lower verte- 
brates, such as the cod fish, it 
is stated that of six million eggs 
spawned, less than a third are 
fertilized. In birds and mam- 
mals, a limited number of eggs 
are matured at one time. 
Sometimes a single ovum de- 
velops at the expense of others. 
Marshall quotes Aral to the effect that the ovary of the rat at birth 
contains 35,100 ova, which are reduced by degeneration to 11,000 
after 23 days, and to 6,000 by the 63d day. Smith and Engle, by 
the implantation of anterior hypophyseal substance in infantile 
female mice, succeeded in inducing the ripening of ova such that 
one of the animals produced twenty young. (See Hypophysis, 
p. 448.) 

The Nervous System. — There are two main groups of activities 
in the vertebrate organism which have determined the general plan 
of organization of the nervous system. 

Reactions toward the external world consist In the finding and 
capturing of food, fighting with other animals, preparing nests or 




Fig. 



150. Human embryo at six weeks. 
(Photo by Newton Miller.) 



MAMMALIA— PHYSIOLOGY 



465 



homes for protection against the physical elements, and many minor 
reactions such as changes in heat, light or moisture. 



Period of Gestation ' 



Mammalia 




Gestation Period 


Condition of Young at Birth 


Monotremata 








Ant eater 






Hatched from eggs. Very 
immature. 


Marsupialia 








Kangaroo 






Size of small rat and very help 
less. Sheltered in pouch. 


Rodentia 








Rat 




21 days 


Eyes closed, small, helpless. 


Mouse 




21 days 




Rabbit 




28-32 days 




Guinea pig 




62-80 days 


Development far advanced. 
Eats corn in 2 or 3 days. 


Ungulata 








Blackfaced sheep 




21 or 22 weeks 


Well advanced but suckling 
some time. 


Cattle 




9 months 




Pig 




16 weeks 




Mare 




II months 




Elephant 




20 months 


W'ell advanced. 


Camel 




45 weeks 




Cetacea 








Whale 




10 months 




Porpoise 




10 months plus 


Young able to follow mother 
about. 


Carnivora 








Cape hunting dog 


{Lycaon) 


80 days 


Lustier than dog. 


Wild dog {S. America) 


2 mos. (59-63 days) 


Young helpless. 


Domestic cat 




56-63 days 




Wild cat 




68 days 




Lioness 




15 to 16 weeks 




Tigress 




22 weeks 




Puma 




15 weeks 




Brown bear 




7 months 




Grizzly 




8 months 




Ferret 




40 days 




Polecat 




40 days 




Walrus 




I year 


Lactation two years. 


Primates 








Monkeys 




7 months 





Man 



280 days 



* Compiled from F. H. A. Marshall, 1922, Physiology of Reproduction. 



466 



MAMMALIA— PHYSIOLOGY 



The internal activities include all the processes related to metab- 
olism, the distribution of nutritive material to various parts of the 
organism, and the various processes connected with the formation 
of the reproductive elements and the nutrition of the embryo. 

Sensory Nerves. — The nerve fibers and central mechanisms which 
have to do with the stimuli affecting the welfare of the animal in 
its surroundings are the somatic afferent or somatic sensory division 
of the Nervous System. 



Lombdoidal rid<je — 
Interpariefal 



Zygomatic process 
of frontal 

Supraorbital ridgs — 



Lachrymal 
fnfra-orbilol foramen 



Nosal capsule 
Maxillary 




Suprooccipital 
Sa(jittal ridge 



— -V ¥\ Porie tal 



Temporal 

Zygomatic process 
of temporal bone 

— Jj Temporal fossa 

^Frontal process 
of malor 

—Zygomatic arch 

ti/lalar 

Supraorbital ridge 

— Orbit 

__Zygomotic process 
of maxillary bone 

■Lacfirymal foramen 
Nasal 
— Foramina incisa 

— i- — -yf-l- Anterior nores 



— Infermoxillory 

Fig. 251. Dorsal view of the skull of the cat. (Drawn by W. J. Moore.) 

All the nervous structures concerned with impulses arising in 
the viscera, in the taste organs, and in the olfactory organ are 
closely related and constitute the visceral afferent or viscer0->sensory 
division of the nervous system. 

Motor Nerves. — All the usual movements of locomotion, of 
offense and defense are directed ordinarily in response to stimuli 
from without. Somatic movements are also performed in response 
to gustatory and olfactory stimuli and have for their object the 
capturing of food. In general, while somatic movements may be 
called forth by visceral stimuli, they are more typically called forth 
by somatic stimuli, and are more precise when they are directed 
in response to them. 



MAMMALIA— PHYSIOLOGY 467 

The nerve centers and peripheral nerves which direct somatic 
movements constitute a distinct portion of the Nervous System 
which we may call the somatic {efferent) motor division. 

The visceral activities consist of contractions of the visceral 
muscles, secretory processes and vaso-motor regulation. All these 
contribute directly or indirectly to the processes of nutrition in 
the widest sense or of reproduction. Just how far they may be 
called forth by somatic stimuli is not known. We know that the 
sight of food may cause salivary secretion. Respiration is called 
forth by rise in temperature within the body. The nerve centers 
and fibers which control the activities of the viscera make up the 
visceral efferent or viscero-motor division of the Nervous System. 

To summarize, in any vertebrate animal there are four kinds of 
nervous activity: (i) Reception of somatic stimuli. (2) Direction 
of somatic movements. (3) Reception of visceral stimuli. (4) 
Direction of visceral movements and activities. 

The mammalian brain exhibits marked superiority over that of 
the lower vertebrates in the development of large richly convoluted 
cerebral hemispheres and a cerebellum not surpassed in any form 
except the bird. The olfactory lobes situated ventrally at the ante- 
rior portion of the cerebral hemispheres are highly developed in 
many of the lower mammals. In common with the reptiles and 
birds, the mammals have 12 pairs of cerebral nerves. There are j/ 
pairs of spinal nerves in man, and 38 pairs in the cat. 

Both the brain and the spinal cord consist of gray and white 
nervous matter but in the brain the gray is on the outside and the 
white is within while in the spinal cord the gray is on the inside and 
the white is external. White matter is chiefly composed of nerve 
fibers while gray matter is much more vascular and composed of 
nerve cells which give rise to nerve fibers. Nerve fibers are non- 
medullated — {a) Naked axis cylinder, {b) Axis cylinder with primitive 
sheath, and medullated — {c) Primitive sheath absent, {d) Primitive 
sheath present. Medullated fibers are present in greater quantity 
than non-medullated in the cerebro-spinal system. The mass of 
white substance of the brain, spinal cord, and optic nerve has 
medullated fibers without the primitive sheath. Both brain and the 
spinal cord are covered by three membranes, the outer dura mater 
with a thin delicate membrane, the arachnoid^ which serves as a 
sheath for the nerves and is separated from the dura mater by a 
narrow sub-dural space. A vascular membrane, the pia mater^ is 



468 



MAMMALIA— PHYSIOLOGY 






si 






^o'-S^^^f ^ 















^ 


^§ 2 


•5 


■? 




t> ^ 


to 


8 


«^ 


^1' 


o 



'0 





"S 


V\ 


a 


C 


O 


SS ^ 


^^ 


c^ 



o 
o 




MAMMALIA— PHYSIOLOGY 469 

loosely connected with the arachnoid by strands of connective tissue 
forming a spongy network but there is considerable space between 
the two called the sub-arachnoid space. This space contains a fluid 
called the cerebro-spinal fluid which differs from ordinary lymph (i) 
in its small per cent of proteins, (2) in the absence of cells and (3) 
in the absence of a fibrin ferment. 

Cerebro-spinal fluid is colorless and alkaline, having a specific 
gravity of between 1,006 and 1,008. It consists mostly of water. 
The solids include a trace of protein, chiefly globulin; if the mem- 
branes of the brain or cord are inflamed, there is much more protein 
present. A small amount of carbohydrate as glucose and the salts 
found in blood plasma occurs, with occasionally a few leucocytes and 
a large quantity of CO2. It contains no antitoxins, opsonins, nor 
alexins which are present in blood plasma and in tissue fluid. 

Cerebrwn. — Much of the cerebral cortex is occupied by large tri- 
angular cells called pyramidal cells, the largest of which is one-six 
hundredth of an inch. These cells are agents in the psychic activity 
of the cortex.^ Cajal called them psychic cells. The fibers of white 
matter of the cerebral hemisphere consist of projection fibers and 
association fibers. The projection fibers are those which project the 
impulses of the outside world upon the sensorium, or the reverse. 
These are cortico-afferent^ leading from lower levels to the cortex, or 
cortico-efferent, leading from the cortex to lower levels. The associa- 
tion fibers which correlate cortical areas are of two types, the arcuate 
which correlate areas of the same hemisphere, and the commissural 
which correlate areas of the opposite hemisphere. The most impor- 
tant commissures in the mammalian brain are the corpus callosiim 
and the anterior^ middle and posterior commissures. The fibers of 
the cortex myelinate late, none receiving the medullary sheath in the 
human brain until the ninth fetal month. (See page 479.) 

Cerebellum. — The cerebellum, important in coordination, con- 
sists of an outer clear gray molecularlayer with an inner reddish gray 
granular layer. At the junction of these two layers are the large 
flask-shaped cells called the Purkinje cells. It is by contact and not 
by continuity of structure that nervous impulses are transmitted. 
The system of the cerebellum shows not only this but shows that 
different parts of the same cell may be supplied with terminal fibers 
from quite different sources. 

8 "Learning without thought is labor lost; thought without learning is perilous." 
Confucius. 



470 



MAMMALIA— PHYSIOLOGY 



Table of Cerebral Nerves and Their Components in Mammals 



No. 



I. 

II. 

III. 



IV. 



VI. 



Name 



Olfactory 
Optic 



Oculo- 
motor 



Patheticus 
or Tro- 
chlearis 

Trigeminal 



Abducens 



Components 



Special viscero- 
sensory 

Special somatic 
sensory 

Special somatic 
motor 



General viscero- 
motor 



General somatic 
sensory 

Special somatic 
motor 

General somatic 
sensory 

Special viscero- 
motor 



General somatic 
sensory A. Ex- 
teroceptive 



Cells of Origin 



General somatic 
sensory B. 
Proprio- 
ceptive 

Special somatic 
motor 

General somatic 
sensory 



Nasal mucous 

membrane 
Ganglion cells of 

the retina 

III. Nuc. at lev- 
el of sup. coll. 



Nuc. of Edinger- 
Westphal 



IV. Nuc. at lev- 
el inf. coll. 



Motor V nuc. 



Semilunar gan- 
glion. (Gas- 
serian g.) 
Periph. br. to 
skin, mucous 
m. of head; 
central br, to 
brain 

Mesencephalic 
V 



VI. Nuc. dors, 
pons. 



Distribution 



Mitral cells of olfactory bulb. 

External geniculate, pulvinar 
of thalamus; superior collicu- 
lus. 

Superior, inferior, internal rec- 
ti and inferior oblique mus- 
cles; levator palpebra supe- 
rior. 

Preganglionic fibers to ciliary 
ganglion, postganglionic fi- 
bers to intrinsic muscles of 
eye. 

Mixed with motor fibers of 
four muscles. 

Superior oblique muscle. 

Mixed with motor fibers to 
superior oblique muscles. 

Mandibularis nerve to tempo- 
ral, masseter, external and 
internal pterygoid, tensor 
palati, tensor tympani, ante- 
rior belly of digastric and 
mylo-hyoid muscles. 

Ophthalmic, maxillary and 
mandibular nerves. 



Mixed with motor fibers to 
masticatory muscles. 

External rectus muscle. 

Mixed with motor fibers to ex- 
ternal rectus muscle. 






MAMMALIA— PHYSIOLOGY 47 1 

Table of Cerebral Nerves and Their Components in Mammals — Continued 



No. 



VII. 



VIII. 



IX. 



Name 



Facial 



X. 



Acoustic 



Glosso- 
pharyn- 
geal 



Vagus or 
Pneumo- 
gastric 



Components 



General viscero- 
motor 



Special viscero- 
motor 

General viscero 
sensory 

Special viscero- 
sensory 

Special somatic 
sensory 



General viscero 
motor 



Special viscero- 
motor 

General viscero- 
sensory 

Special viscero- 
sensory 
Somatic sensory 

General viscero- 
motor 

Special viscero- 
motor 



General viscero- 
sensory 

Special viscero- 
sensory 

General somatic 
sensory 



Cells of Origin 



Salivat. sup. 
nuc. 



Motor VII nuc. 

Geniculate gan- 
glion 

General gan- 
glion 

A. Vestibular 
ganglion. B. 
Spiral gan- 
glion of cochlea 

Motor IX root. 
Nuc. saliva- 
tory inf. 

Nuc. ambig. 

Ganglion pe- 
trosal IX 

Ganglion 
petrosal 

Ganglion supe- 
rior IX 

Dorsal motor 
nuc. of X 

Nuc. ambiguus 



Ganglion 
nodosum 

Ganglion 
nodosum 

Ganglion 
jugulare X. 



Distribution 



Preganglionic fibers in chorda 
tympani; postganglionic fi- 
bers from sub-maxillary gan- 
glion to submax. and sub- 
lingual glands. 

Stapedius, posterior belly of 
digastric, stylohyoid muscle. 

Sup. petrosal, chorda tympani, 
tympanic plexus. 

Chorda tympani and lingual 
nerve to taste buds on ante- 
rior two-thirds of tongue. 

Semicircular canals, sacculus, 
utriculus. 

Organ of Corti of Cochlea. 

Preganglionic fibers in tymp. 
and sup. petrosal nerve; 
postganglionic from otic gan- 
glion to parotid gland. 

Stylopharyngeus muscles. 
(Unstriped pharyng.) 

Sensory fibers to pharynx, 
posterior one-third of tongue. 
(Lingualis IX.) 

Tastebuds of post, one-third of 
tongue. 

Tactile corpuscles of posterior 
one-third of tongue. 

Preganglionic sympathetic fi- 
bers to pharynx, stomach, 
heart, lungs, trachea. 

Superior and inferior laryngeal 
and pharyngeal nerves to 
striated muscles of pharynx 
and larynx. 

Nerves from viscera, larynx, 
pharynx, lungs, heart, and 
sympathetic connections. 

Internal laryngeal nerve. 

Ramus auricularis vagi. (Be- 
hind ear.) 



472 



MAMMALIA— PHYSIOLOGY 



Table of Cerebral Nerves and Their Components in Mammals — Continued 



No. 


Name 


Components 


Cells of Origin 


Distribution 


XL 


Spinal 


General viscero- 


Dorsal motor 


Preganglionic fibers distrib- 




accessory 


motor 


nuc. of X. 


uted with the vagus. 






Special viscero- 


Nuc. ambiguus 


Striated muscles of pharynx 






motor. 




and larynx and rami to tra- 
pezius and sterno-cleido-mas- 
toid muscles. 


XII. 


Hypo- 


Special somatic 


XII. nuc. 


Hypoglossiis nerve to muscles 




glossal 


motor. 




of tongue. 



In the I, II, III, IV, VI, and VIII nerves the organs of special sense are supplied, 
while the V, VII, IX, X, and XI cerebral nerves have visceral functions predominating. 

Consult Johnston's Comparative Neurology and article by C. J. Herrick in Refer- 
ence Handbook of Medical Sciences, entitled the Cranial Nerves. 



The bodies of Purkinje cells are surrounded by the basket ter- 
minals of the stellate cells of the molecular layers, while their proto- 
plasmic processes are in contact with the efferent fibers that arise 
from more distant portions of the nervous system. 

Medulla Oblongata. — The medulla oblongata controlling heart 
beat and respiration, the enlarged anterior portion of the spinal cord, 
sends off the cerebral nerves from the fifth to the twelfth inclusive. 
It receives columns of fibers originating in the spinal cord and may 
be considered a great switch station for impulses passing up and 
down the cord. 

Spinal Cord. — In all vertebrates having well-developed limbs 
the two regions of the spinal cord with which the nerves of the limbs 
are connected are somewhat thicker than the rest of the cord and are 
known as the thoracic and lumbar enlargements. Each of the 
spinal nerves has a ventral anterior root and a dorsal posterior root 
with spinal ganglia, containing nerve cells and fibers which are 
usually afferent., conveying impulses from the parts and organs of 
the body to the central nervous system. The vetttral root is not 
ganglionated and its fibers are efferent, conveying impulses from the 
neuron outward. The cranial nerves are twelve in number on each 
side in reptiles, birds and mammals. Only the trigeminal or fifth 
present a double-rooted arrangement similar to a spinal nerve. 
Several however have ganglia comparable to those of the dorsal 
roots of the spinal nerves. Besides the fifth or trigeminal these 



MAMMALIA— PHYSIOLOGY 



473 



include the seventh (facial), eighth (auditory), the ninth (glosso- 
pharyngeal) and the tenth (pneumogastric). 

Origin and Structure of the Neuron. — A neuron consists of a cell 
body with all of its processes. The entire nervous system is com- 
posed of cells with one or more processes. These cells develop early 
in embryonic life from certain ectodermal cells (neuroblasts) of the 
neural canal (which is formed by a dorsal invagination of the ecto- 
derm). The neuroblasts develop secondary processes, many in the 
neural canal, others after wandering from it, and by this process 
of budding become nerve cells. The primitive processes continue 
to extend until they reach the periphery of the body, are invested 
with medullary sheaths supplied by connective tissue of the region 
through which they pass, and become nerve fibers. Nerve fiber and 
nerve cell are therefore parts of the same histological unit. 

The processes are of two kinds: i. («) unbranched; {}?) uniform 
in diameter with lateral offshoots called collateral branches. These 
are generally the central part of a nerve fiber and are called neurites 
or axones. i. Processes which branch soon after leaving cell body 
and break up into smaller branches called dendrites. Thus the 
neuron consists of a cell body containing a conspicuous nucleus, 
nucleolus and cytoplasmic granules, protoplasmic processes called 
dendrites, an axis cylinder process which passes into a nerve fiber, 
and a final termination in the form of a branching tuft. Golgi's 
idea that protoplasmic processes or dendrites subserve nutrition of 
the cell is without foundation. Many circumstances show that they 
transmit impulses. 

The Sympathetic Nervous System consists of a pair of elongated 
ganglionated cords extending from the base of the skull to the lumbo- 
sacral region, connecting on the one hand by a series of branches to 
the spinal nervous system, and on the other hand giving off an irregu- 
lar series of branches to the viscera. At its cephalic end, each sym- 
pathetic cord is continued in a plexiform manner into the cranial 
relationships with certain cranial nerves. Caudally, the two cords 
are joined by fine filaments and connected by the coccygeal ganglion. 

The sympathetic system rearranges and distributes fibers, derived 
from the cerebro-spinal system, to the viscera and vessels of the 
splanchnic area. It transmits afferent fibers from the viscera to the 
cerebro-spinal system, and sends fibers to the vessels, involuntary 
muscles and glands in the course of the somatic divisions of the 



474 MAMMALIA— PHYSIOLOGY 

spinal nerves. Its fibers are called white rami communicantes 
(medullated) and gray rami communicantes (non-medullated). 
Sense Organs. — 

Kulpe's Classification of Sensations by Organs i" 
1. Vision, 
1. Audition. 

3. Cutaneous. 

Cold 
Warmth 
Pressure 
Pain 

4. Olfactory. 

5. Static sense. 

Ampullar (dizziness) 
Vestibular 

6. Gustatory. (See page 477.) 

7. Kinaesthetic. 

Muscular 

Tendinous 

Articular 

8. Organic. 

Hunger 
Thirst 
Nausea 
Suffocation 

9. Reproductive. 

Vision depends on the proper function of the complicated eye. 
Sensation passes from the layer oirods and cones of the retina through 
its nuclear and molecular layers to the ganglion cells from which 
nerve fibers transmit the impulse to the optic tracts leading to the 
brain. (See p. 468.) 

Visual sensations include hue or quality, brightness and satura- 
tion. The stimuli are the ethereal vibrations ranging between 
400,000 and 800,000 billions per second. Color is stimulated 
by the wave length while the height of the wave gives the bright- 
ness and the form of the wave determines the degree of saturation. 
■It is said that in certain tapestries in Milan there are 1,800 colors 
while in some Italian mosaics there are 30,000 colors. ^^ 

Color Blindness. — Some people are unable to distinguish all of 

1° Consult Murchlson, C. 1929. The Foundations of Experimental Psychology. 
Clark Univ. Press. 

11 Consult Herrick, C. J. 1931. Introduction to Neurology. W. B, Saunders. 



MAMMALIA— PHYSIOLOGY 



475 



on. 



the 1 60 color tones. In total color blindness one cannot distinguish 
between any other colors than gray. Partial color blindness is the 
inability to distinguish between a certain group of colors. 

Audition. — The mammalian ear receives sound waves and trans- 
mits them by the tympanum to the ossicles and from the ossicles 
by way of the vestibule 
they pass to the liquid 
in the cochlea. The 
movement is continued 
to the basilar membrane 
where vibrations of the 
fibers in unison with the 
tone affect definite hair 
cells and the sensation is ^ 
transmitted to the brain 
by way of the eighth 
nerve. (See p. 468.) 

The Organ of Corti 

in the cochlea of the ear 

is the receptor involved 

in hearing. Numerous 

theories of the activa- , , 

c -i -^ ^ Fig. au. The vertebrate eye. a, aqueous hu- 

tion of the constituents ^-^ . . „ i u -^ ; ■,,;.. 

. ^ mour; c, conjunctiva; C, cornea; ch, choroid; /, ins; 

of this organ by the Vl- ^^ j^^^. ^_„^ ^p^j^, ^erve; P, pigment layer; p, pupil; 
brations of fibers imbed- r^ retina; r, layer of rods; s, sclerotic; y, vitreous body. 
ded in the basilar rnem- (From Kerr. Courtesy of Macmillan and Co., Ltd.) 
brane have been ad- 
vanced. The human ear is sensitive to vibrations with a frequency 
of from thirty to thirty thousand per second. 

Hearing in Aquatic Mammals. — The whale., like the seal and the 
porpoise, lacks external ears. It has blow-holes on the top of its 
head, which are closed by means of elastic cartilage valves. The 
cachalot has an external opening, about i inch long in the full-grown 
whale. The external auditory tube is closed by bony growth, 
protecting the ear drum from the pressure encountered at great 
depths. It is claimed by Kellogg that the whale-bone whales now 
actually hear through their noses, and that the ear drum is nori- 
functional. The bulla, a structure coiled like a conch shell, is said 
to receive the sound waves. Whales are able to detect sounds very 
readily. 




V. 



476 



MAMMALIA— PHYSIOLOGY 



Cutaneous Sensibility. — Besides light touch we have sense organs 
for deep pressure sense and pain. Adjacent to each other there are 
end organs for sensibility to cold and heat. It is said that there 
are over 250,000 cold spots and but 30,000 warm spots. Sometimes 
a paradoxical sensation of cold may be aroused by a hot stimulus. 
The cheek is relatively insensitive to pain. 



^vtox- <y/Qnds 

Cochlea^ \ 

Cowi'ty of ^Ac-jy v< 

ty/nponum or drum — r^^J '"" 




- > 



Auc/ifory 
ccfno/ 
ancf 
tvo//S 



—-Sty/oid pr-Qcess 

- • Internal corofid artery 



/Auditory tube 



Fig. 254. Diagram of the human ear. (After Morris. Courtesy of P. Blakiston's 

Son & Co.) 



Olfactory Sense. — Olfactory sensations are served by the nasal 
mucous me?nbra7te which has end-organs leading to the olfactory 
nerves. The end organs for the sense of smell are limited to the 
upper part of the nasal cavity. The epithelial layer consists of 
columnar supporting cells and several layers of nerve cells which 
are elongated in shape and nucleated. The prolongation of the 
Q^W peripherally between the columnar cells terminates at the surface 
in from six to eight hair-like processes while the central prolongation 
continues as a non-medullated nerve fiber to the olfactory lobe where 
it arborizes in relation to the dendrites of certain " mitral cells " 
whose axones transmit impulses by the olfactory fibers. 

Static Sense. — The organs of equilibration are the semicircular 
canals of the internal ear. 

Gustatory Sense. — The organs of taste consist of sensory cells 
found in the taste buds of certain papillae on the tongue. (See page 



MAMMALIA— PHYSIOLOGY 



477 



429.) There are four types of taste: Sweet, sour, salt and bitter. 

In eating one receives sensations from taste, smell, cutaneous sense 

and temperature sense. The child prefers sweets while sour and 

bitter are unpleasant. Children have more taste organs than the 

adults since some of the taste buds atrophy as age advances. One 

section of the tongue is wholly insensitive to taste. The anterior 

portion of the tongue is sensitive to sweet substances, the lateral 

portions are sensitive to sour and salt, while 

the posterior portion is extremely sensitive to 

bitter substances. 

Kinaesthetic Sense. — Certain kin aesthetic 

sense organs are contained in the skeletal 

muscles, tendons and joints and transmit to 

the brain knowledge of positions of parts of 

the body. 

Organic Sensations. — Many subconscious 

sensations concerned with visceral activities 

are carried to the brain by the aid of organs 

connected with the digestive, respiratory and 

circulatory systems. Unusual stimuli may 

produce thirst, hunger, nausea or suffocation. 
Weight of the Brain. — The brain of the 

average adult human female weighs 44.5 

ounces and that of the male 49.75 ounces. 
Cases have been recorded in which the brain 

attained a weight of 74.8 ounces, one case 

being that of an idiot. The weight of the 

brain of the gorilla is 15 ounces. In the 

healthy body the relation of the weight of tesy of Henry Holt & Co.) 

the human brain to that of the body is 1-41. 

Transmission of an Impulse. — From a sense organ in the skin an 
impulse passes to the sensory fiber of a spinal nerve, in at the dorsal 
(posterior) root to the dorsal horn of the cord and to a spinal sensory 
cell. Thence it goes up the dorsal column to the sensory cell of the 
optic thalamus. From the optic thalamus it passes to the sensory 
cell of the cortex in the localized area indicated by its original source. 
Then the impulse to act, beginning at the motor cell of the cortex, 
passes across to the motor cell of the corpus striatum (see Figure 
256), thence down the anterior ventral colujnn of the spinal cord to 
a spinal motor cell in the ventral horn, out at the ventral root of the 




Fig. 255. Upper sur- 
face of the tongue. /, 
circumvallate papillae; 2, 
fungiform papillae. (After 
Brubaker, from Kellogg, 
Animals and Man. Cour- 



478 



MAMMALIA— PHYSIOLOGY 



Afferent or sensory neurone 
Gray mafrer / 

Spinal cord j ' /n 



~\—5k/n 




Receptor 



White matter 



\ Efferent or motor neurone 

\ 
Ad JUS tor neurone 



Fig. 256^^. Reflex arc. (Drawn by W. J. Moore.) 



-Ef fee for 



Olfactory — -^ 




-Cerebro - cortex 



Coudotum 

Corpora striata 

— Lenticula 

— Tfiaiamus 



Corpora quodrigennina 
nucleus 



— -Substantia nigra 



'erebei/o - cortex 



Olive 



Fig. 2565. Chief ganglionic categories. (After Spitzka.) 



MAMMALIA— PHYSIOLOGY 479 

cord to a spinal nerve and thence to the proper muscle. As many 
of the fibers cross to the opposite side, we find that a lesion of the 
brain on the right side will cause paralysis on the left side of the body. 

Reflex Action. — In a simple reflex, we never find as few as two 
neurones involved. The impression from the sensory cell passes 
into the spinal cord and from the spinal sensory cell across (by two 
or three intermediate neurons) to the spinal motor cell. Thence it 
passes to the proper muscles. Sensation and reaction are almost 
immediate and the proper movements have been made without 
awakening consciousness in the cerebrum until later. 

A Triumph of Coordination. — A celebrated pianist has actually 
been ascertained by Sir James Paget to have played 5,995 notes in 
four minutes and three seconds. Paget estimated that there were 
at the rate of 96 transmissions of force from the ends of the nerve 
fibers along their course to the brain, in each of the same seconds 
during which there were 72 transmissions going out from the brain 
along other nerve fibers to the muscles. The notes were played in 
due time and place, and with the sentiment of the music. (J. A. 
Med. A.) 

Fatigue in the Nerve Cell — In some important studies made a 
number of years ago (1892) Hodge demonstrated the effects of 
fatigue on the nerve cell. He showed that after prolonged stimula- 
tion of a nerve fiber its cell body and nucleus tended to shrivel, and 
degeneration of the cytoplasm became apparent. The whole 
structure might be compared to a shriveled apple. Later studies 
by DoUey ^^ confirm Hodge's conclusion. There is only slight evi- 
dence of increased CO2 in the nerve fiber after stimulation. 

Regeneration in the Nervous System. — Since there is no neu- 
rilemma in the spinal cord and in the brain there is no complete 
regeneration. The nerves of the body will readily regenerate, 
provided the nucleus of the nerve cell is uninjured. 

Myelination. — Recently the entire process of myelination of 
nerve fibers ^^ has been seen by Speidel (J. of Exp. Zool. in press) in 
the transparent tail fin of living frog tadpoles. Individual nerve 
sprouts and sheath cells were watched for long periods (ten days to 

12 Hodge, C. F. 1892. Jour, of Morphol., vol. 7; Jour, of Physiol., 1894, vol. 17. 
Dolley, D. H. 1917. Jour. Comp. Neurol., vol. 27, pp. 299-324. 

13 Nerve cells and sheath cells may readily be cultivated in vitro, and the growth of 
nerve fibers observed, but the formation of the myelin sheath has never been obtained 
in artificial media. 



48o MAMMALIA— PHYSIOLOGY 

several months). Primitive sheath cells on the early unmyelinated 
nerves multiply and migrate to the advancing "myelin-emergent" 
sprouts and myelin segments are added distally in an orderly man- 
ner. Each segment is formed through the combined action of a 
sheath cell and a myelin-emergent fiber. Myelin of a segment first 
appears near a sheath cell nucleus and extends progressively in both 
directions. Unmyelinated gaps between adjacent myelin segments 
may be filled in later by the intercalation of new segments. End-to- 
end anastomosis of segments sometimes occurs with complete ob- 
literation of the intervening node of Ranvier. A portion of one 
segment may be appropriated by another segment, accompanied 
by the establishment of a new node. (Courtesy of C. C. Speidel.) 

Hibernation and Aestivation in Animals. — Certain amphibia, 
reptiles and mammals are able to go into a sleep when the tempera- 
ture falls. Hibernation is marked by a reduction of all body proc- 
esses to the minimum. For example, the hibernating dormouse 
periodically takes a dozen respirations, then ceases breathing for 
several minutes. Normally, when awake, it respires at the rate of 
80 times a minute. A summer resting period, known as aestivation^ 
is characteristic of the mudfish {Protopterus) and of certain amphibia, 
reptilia, and a few mammals. 

Organs That Man Can Lose. — A leg, an arm, an eye, his tonsils, 
gonads, spleen, appendix, gall-bladder, part of his lungs, part of 
his brain, and as much as twelve feet of his intestine may be re- 
moved without serious results*. Entire lobes of the lungs have been 
removed, with beneficial result?. 

Statistics of Vitality. — Muscles of the human heart are alive 2 
hours after normal heart beat and respiration have ceased. The 
body muscles are alive 5-6 hours thereafter. Muscles of a rabbit 
will live Zyi hours after the death of the animal. Those of a sheep 
survive io>^, those of a dog 11^ and those of a cat I2>^, those of a 
frog 24-30 hours. 

Susceptibility of Mammals to Poison. — The porcupine or 
" hedgehog " takes with apparent enjoyment a dose of cantharides 
that will kill several persons under excruciating pains. In rabbits 
and dogs, morphine causes vomiting and then light sleep, but more 
depression in the rabbit. The rabbit can take more morphine than 
can a man fifty times the animal's weight. Morphine first causes 
wild excitation in the cat and other Felidae and then depression of 



MAMMALIA— PHYSIOLOGY 48 1 

the intelligence. Small doses of tnorphine produce sleep in the goat, 
horse and ass. Amygdalin does not affect dogs, but kills rabbits! 
An especial degree of tolerance to atropine is found in the herbivora.* 
Atropine effects pass off in rabbits' hearts sooner than in other 
animals by the active decomposition of the alkaloid which occurs 
in their plasma. Rabbits are not susceptible to belladonna. Rats' 
hearts are much less susceptible than rabbits' to digitalis. Doses 
of lead and nicotine sufficient to kill a man do not injure the goat. 



CHAPTER XXI 

Social Life of Animals 
Association of Different Species 

Living Free. — Free living forms are those that are at liberty to 
range independently. They feed upon animals, and are then called 
carnivorous^ or they feed upon plants, usually destroying them 
although not necessarily causing their death, and are called herbiv- 
orous. 

Commensalism. (Lat. com^ together; and mensa, table.) — 
Commensalism as we shall treat it consists in an association for 
mutual benefit less permanent than symbiosis. Commensalism 
may be for protection, transportation ov food. 

The best known example of commensalism is the case of the 
hydroid colony living on the shell of a hermit crab. As the hydroid 
furnishes the crab with camouflage and protects it from enemies by 
the use of its stinging cells, it renders some service in return for 
transportation and for particles oi food broken up by the crab. 

Symbiosis. (Gr. syn, together; and bios, life.) — The term 
symbiosis has by some been applied to all intimate associations 
between organisms (including parasitism); by others to relations 
between organisms in which benefits are mutual; and by still others 
to plants living within the body of animals in a presumably beneficial 
relationship. Until recently, zoologists considered symbiosis in 
the broad sense, holding that it refers to ani7nals or plants living 
together for mutual benefit. It is now applied to relationship be- 
tween plant and animal; animal and animal; or plant and plant; it 
always being understood that no parasitism occurs. Lull calls it 
the most intimate association for ynutual benefit, an extremely close 
commensalism. We shall consider symbiosis in the latter sense. 

Symbiosis may be between a green chlorophyll-bearing plant 
and an animal; between a chlorophyll-bearing plant and a colorless 
one; or between two animals. Bacteria living in the digestive tracts 
of animals are to be considered as an example of symbiosis since they 
seem beneficial. Certain ruminants, apes, and South American 
rodents are able to digest cellulose by means of the Ophryoscolecidae, 

482 



SOCIAL LIFE OF ANIMALS 483 

which are ciliated Protozoa inhabiting their digestive tracts (p. 30). 

An example of animal-animal symbiosis is the case of termites 
which live in beneficial relationship with the flagellates, Tricho- 
nympha and allied genera (p. 29). 

Parasitism. (Gr. para, beside; sitos, food.) — In Biology, 
parasitism is the condition of an organism which obtains its nourish- 
ment wholly or in part from the body of another living organism 
and which usually brings about some modifications in both guest 
and host. In true parasitism, the bodies of the host and the parasite 
must be in temporary or permanent contact other than that in- 
volved in preying and capturing. The presence of the parasite 
must not be beneficial. Ectoparasites may be temporary such as 
plant lice, caterpillars, mosquitoes, flies and the leech; or permanent, 
such as bird lice (for the bird), body lice and chigoes (chiggers). 
Endo-parasites include intestinal worms like the tapeworm, hook- 
worm, and pin- worm; and blood parasites such as the malarial 
sporozoan and the filarian worms. 

The Effects of Parasitism. — i. On the Parasite. — Any parasite 
may undergo some degeneration. In many cases, little remains 
but the reproductive apparatus. 

1. On the Host. — The host may be very resistant, and by gather- 
ing extra food render the parasite harmless; many white blood 
corpuscles may be assembled and carry away the organisms. The 
host may enclose the parasite in a cyst; it may develop counter 
poisons, killing the parasite; or anti-bodies may neutralize the 
injurious substance formed by the parasite. The host, for some 
time apparently uninjured, may have its resistance so lowered by 
the rapid multiplication of the parasites that it will succumb to 
what ordinarily might be a minor ailment or injury.^ 

Association of the Same Species 

Colonies. — (i) Certain hydroids have a diverse differentiation 
of the individuals. Coelenterate polyps are modified for feeding, 
reproduction and locomotion. (2) The " Portuguese Man of War " 
has specialized structures for feeding, reproduction and protective 
and aggressive activities. (3) Sponges have cellular differentiation 
for protection, ingestion, storage, distribution of food and reproduc- 

^ See Stunkard, H. W. 1929. Parasitism as a biological phenomenon. Sc. 
Men., vol. 28, pp. 349-362, April. 



484 SOCIAL LIFE OF ANIMALS 

tion. Some biologists are disposed to regard the higher organisms 
as colonies of lower forms. 

Communities. — (i) Bees have a queen (reproductive), the male 
drones (reproductive) and the workers which are only short-lived 
laborers. The chosen queen is fed " bee bread." (See Sex Deter- 
mination, page 533.) (2) Termites or " White ants." The workers 
are small, blind, wingless, pale in color and sexually immature but 
with strong jaws. The " soldiers " are blind, wingless, immature but 
have highly developed scissors-shaped jaws and an enlarged head, 
both heavily chitinized and darker in color than the rest of the body. 
The complemental females and males are blind, wingless, and not 
completely mature, but may develop to supplement in the produc- 
tion of young if the true sexed individuals are not sufficient. The 
true or chief females and males are darker in color than the other 
castes, winged and with well-developed visual organs. They live 
above ground; the others are either subterranean or with covered 
tunnels. (3) True ants consist of winged males Q.nd females, workers 
and soldiers. We find that there is a social evolution in ants as in 
man. (Wheeler.) Foraging or maraudifig ants, like Ecitor, have 
officers and scouts. Slave-holding ants, like Polygerus, have become 
unable to dig, care for their young, or store up food without slaves. 
The herding ants live in beneficial association, keeping aphids for 
their milk, " honey dew." The harvester ants store up grains and 
seeds. The thief ants {Solenopsis molestd) feed on the larvae and 
pupae of larger ants, escaping into burrows too small for the avengers 
to follow. The commensal ants include Leptothorax emersoni which 
secure food and shelter from Myt-micae brevinoides and in return 
act as barbers and manicures, probably removing parasites and 
keeping their benefactors more healthy. (Wheeler.) 

Gregariousness. — Herds of buffalo, packs of wolves and schools 
of whales collect for protection and food. In sheep, a leader or 
sentinel is characteristic of such groups. The same is true in many 
other animals. Pallas states that the saiga antelopes of Siberia 
change sentinels. In the •#nd reindeer, females act as sentinels and 
are also said to change places when wearied by standing. 

When cattle or even sheep are attacked in the wilds, they form 
a circle with the males and the most powerful females directing their 
horns outward, while weaker females and the young are huddled in 
the center, Man is sometimes less concerned for the welfare of his 
own. 



SOCIAL LIFE OF ANIMALS 485 

Men are not sheep, but they have two of the dominating characteris- 
tics of sheep. They are gregarious and they are easily frightened. 

— Ramsay MacDonald. 

Polygyny (many wives), and Polyandry (many husbands). — In 
the ostrich of South America the cock bird lives with five or six 
hens {polygyny). All the hens lay their eggs in one nest, but incu- 
bation is done by the male alone, and after hatching, the young 
chicks follow the father. Each female cowbird mates with several 
males {polyandry). The female deposits her eggs in the nest of 
another smaller species. (See p. 349.) 

Cases in Which the Sexes Live Apart. — In the case of many 
antelopes the herds divide according to sex between one pairing 
time and another. After the pairing season is over, wild sheep and 
other ungulates live in herds composed of one sex only. In Indian 
and African elephants the sexes form herds of their own, herds of 
females being accompanied by their young and led by a female. 
At breeding time a male temporarily takes possession of a herd of 
females. Migrating salmon travel separately, shoals of males 
appearing first, followed later by the females. The same is true with 
the salt-water minnow {Fundulus heteroclitus). 

Societies Composed of Different Species. — Different species of 
dolphins form groups led by one individual. Wild zebras, asses, 
yaks, and horses are sometimes seen together, while wild buffaloes 
associate with elephants. 

Monogamy. — All species of parrots are monogamous, while 
rose-colored starlings, sparrows, house pigeons and mallards are 
monogamous, but nest gregariously. In the weaver bird two cou- 
ples often share a common nest in which both the hen birds lay their 
eggs and hatch them out. 

Seasonal Mateships. — Seasonal mating occurs in a number of 
beetles, the couples living in associations, not societies. Lions 
choose a fresh mate at each pairing time while in some marten species 
the two sexes live together until afteriUjg young have been reared. 
Foxes live monogamously and the father brings food to the young. 
Wolves, foxes, and bears live mated for a short time. 

Types of Families, (i) Parent Families. — In the wood-boring 
beetles, the parents feed the larvae and watch over the chrysalis. 
Both the male and the female of certain species of fishes guard the 
nest, the hatched young returning to the nest every evening for two 



486 SOCIAL LIFE OF ANIMALS 

or three weeks. Parasitic egg-laying. A South American duck 
{Metopiana) lays Its eggs in the nests of other birds such as the coot 
and sea-gull, while the European cuckoo lays her eggs in the nests of 
other birds. The American cowbird has the same habit of seeking 
foster parents for her offspring. (See Friedmann, H. 1929. The 
Cowbird. C. C. Thomas Pub.) 

(2) Father Families. — The male obstetric frog {Alytes obstetri- 
cans) carries the eggs with him in a long string wound around his 
hind legs until the larvae emerge. The male Rhinodenna carries 
the eggs in his gular vocal sac until the metamorphosis of the young 
is complete. In some species of frogs the tadpoles are carried on the 
back of the male. 

The male stickle-back fish builds a nest and entices several 
females to deposit their eggs in it. Eggs and young are guarded 
by the father. In a number of fish species the male seizes in its 
mouth young that have strayed away and brings them back to the 
nest. It is said that the male Amia (the bow fin) leads its family of 
young for four months.^ 

(3) Mother Families. — The females of some species of leeches 
carry their offspring about, the young attaching themselves to the 
body of the mother with their suckers and always returning to her. 
The female earwig {Forjicula) guards her eggs and young in a hole 
which she digs herself, collecting them together if they get scattered. 
The female mole cricket digs a hole for the eggs and guards them, 
but turns cannibal occasionally. 

In crayfish and spiders the mother carries eggs and young around 
with her. Female scorpions carry young on their backs. In a 
number of species of fish the females lead their young for some time 
after hatching. In some species of Chichlidae the female carries 
the eggs in a pocket on the back and the female Pipa (a toad) carries 
its young in pouches of skin on its back until metamorphosis has 
occurred. ^a^ ^^AitM^M^^ ^p(lU4^^ 

Female crocodilia watch over the eggs^open them by means of a 
well-developed egg tooth, ^|^lead the young to the water. Mother 
families are the rule among birds. Mother families are found in the 
cat family, in foxes, polar bears, and seals. 

(4) Child Families. — Certain processionary caterpillars {Thau- 
matopaea) , emerging from the same mass of eggs, remain together 

2 Consult Gill, Theodore. 1905. Parental Care Among Fresh Water Fishes. 
Smithsonian Rep., pp. 403-531. 



SOCIAL LIFE OF ANIMALS 487 

permanently. Herring of the same spawning form schools which 
remain together permanently. 

References on Animal Relationships 

Alverdes, F. 1927. Social Life in the Animal World. Harcourt, 
Brace & Co., Inc., New York. 

BoRRADAiLE, L. A. The Animal and its Environment. Henry Frowde 
and Hodder and Stoughton. 

Cleveland, L. R. 1926. Symbiosis among animals with special refer- 
ence to termites and their intestinal flagellates. Qu. Rev. of Biol., 
vol. I, no. I, pp. 51-60. 

DoFLEiN, F. 1914. Das Tier als died des Naturganzen, from R. Hesse 
and F. Doflein, Tierbau und Tierleben, Bd. 2. Leipzig and Berlin. 

Elton, C. 1927. Animal Ecology. Macmillan Co., New York. 

Protection 

Masking. — The caddis fly lives in a sand case. Certain crabs 
cut off the tunic of a sea squirt and drape it over their carapace. 
Others plant sea weed on their backs. 

Flounders cover themselves with sand while the toad puffer or 
swell fish distends its body with air and escapes many enemies. 
Other fishes cover themselves with sea weed. 

Color Resemblance. — Temporary alternations of color are due 
to the amount of dilation of chromatophores. In the cuttle fish 
and the squid we find that blushing occurs if they are irritated, 
but they return to normal pale color shortly. 

Fishes, such as the flounder and the minnows, are able to adapt 
themselves to the background. If they are blinded, color change is 
impossible. Frogs, toads and chameleons are able to alter their 
pigment {inelanophores) to suit the background, although Ditmars 
holds that the chameleon is not immediately successful. 

Partridges and ptarmigans change their pigment to suit the 
background. The arctic hare changes from brown to white when 
winter comes. In the mammals we ^pjjgl that change in color de- 
pends on the oxidation of melanin pigment. 

Some animals with a brilliant hue are bad tasting. The ex- 
creted material makes the color bright. The skunk is an example 
of a brightly colored form which has a distinctly obnoxious odor. 

Thayer, Poulton and others have emphasized the influence of 
coloration on the survival of many animals. Except in the arctic 



488 



SOCIAL LIFE OF ANIMALS 



regions we find that the body Is darker on the parts ordinarily Il- 
luminated by the sun and sky, while the most shaded parts are 
usually lighter In color.^ In the tiger and the zebra the colors are 
broken by lines and the animal blends with Its background. During 
the World War, battleships were wonderfully camouflaged by lines 
and patches of alternating light and dark color. 




Fig. 257. Young fawn in mountain laurel, Monongahela National Forest, W. Va. 
(Photo courtesy of U. S. Forest Service.) 

Thayer has pointed out that even In the case of some animals 
that are quite conspicuous to man and seem to stand out against the 
sky, we must remember that the chief enemies of the forms under 
consideration are not tall animals. He once convinced a group of 
zoologists at Woods Hole, Mass., In a striking manner, by having 
them crawl around in the grass, gazing up at life-size card-board 
figures of deer. 

^ Wild cats are striped on the ventral side and hence almost invisible in the trees 
(W. R. B. Robertson). 



SOCIAL LIFE OF ANIMALS 489 

Mimicry. (Protective Resemblance.) — Some butterflies resem- 
ble a leaf, certain beetles mimic the wasp, certain harmless flies 
mimic bees and are preserved from destruction by birds. The 
walking stick insect resembles twigs. Some harmless snakes resem- 
ble in markings venomous forms such as the coral snake. (See 
Fig. 176.) 

References on Animal Coloration 

Beddard, F. E. 1892. Animal Coloration. 

Poulton, E. B. 1890. Colors of Animals. 

Roosevelt, T. African Game Trails. 

Thayer, A. H. 1909. Concealing Coloration in the Animal Kingdom. 

Geographical Distribution 

A similar environment does not always explain the appearance 
of like forms. If we are to accept the theory that all forms are 
derived from a common ancestor, we can readily explain some of the 
following facts: 

(a) The llamas of South America have as their nearest living 
relatives the camels living in the deserts of Asia. In Oregon one 
finds fossil llamas. {^) The Australian kangaroo has no relatives 
nearer than the opossum. Neither is found in its native home, which 
was Europe. How did they reach South America and Australia? 
(c) The plants of Madagascar are not related to those of Europe 
while both plants and animals of North America and Eastern Asia 
are similar. Why? 

Explanation. — Present barriers have not always existed, and 
land connections that once joined continents have disappeared, 
separating closely related forms. Climatic changes have also 
produced cataclysmic effects. 

Dispersal of Small Forms. — In the case of smaller forms, we 
find that dispersal is effected quite readily. Protozoa and the eggs 
and larvae of numerous worms and Rotifers are transported by 
birds and other animals, as well as attached to wind-blown or 
floating debris. It is well known that the glochidia of fresh water 
mussels are carried long distances attached to the gills and fins of 
fishes. 

Again, driftwood bears strange companions to far distant islands. 
Beebe on his Arcturus voyage counted on one floating log 54 species 
of marine crabs, worms and fishes. 



490 SOCIAL LIFE OF ANIMALS 

• 

Barriers. — (i) The salt of the sea proves a barrier to fresh water 
animals. Amphibia are almost never found in salt water. It has 
been found that the salinity of water determines the species of salt 
marsh mosquitoes in a given region, while the Ph of the water is 
apparently important in determining the distribution of Arthropod 
species and of fishes. Sometimes species changes occur as in the 
brine shrimp, Artemia, which alters its characteristics in fresh water 

(p. 170)- 

(2) Elton quotes various authors who have shown that water 

supply is an important limiting factor in determining the ranges of 
wild birds and mammals. In the Burmese forests the occurrence of 
elephants, bufFalos, tigers, panthers, pigs and monkeys is deter- 
mined in dry season by the proximity of water-holes. In the case 
of rooting and digging animals, such as pigs and moles, distribution 
is determined by softness of the ground which of course depends on 
the water supply. In Mesopotamia the black partridge {Franco- 
linus vulgaris) is never found more than a hundred yards from water, 
which it requires for drinking purposes. 

(3) Depth of water proves an effective barrier. Certain of the 
shore fishes of Hawaii are not found in the waters of California. 

(4) Temperature proves most powerful in preventing the dis- 
persal of many animals and plants. Some animals are found in 
hot springs or in the Arctic ice, however. 

Dr. Nellie Payne has given us important information on the 
survival of insects at low temperatures. Consult Payne, N. M,, 
1926 (Freezing and Survival of Insects at Low Temperatures, 
Quart. Rev. of Biol., vol. i, pp. 270-282). Brues, C. T. (Animal 
Life in Hot Springs, Qu. Rev. of Biol., vol. 2, no. 2, pp. 181-203, 
June, 1927), has summarized the literature and shown that Ameha 
Umax was found in water at 50° to 52° C. (ii2°-i26° F.), while 
Ciliates were found in water at 46° C. (115° F.). The crustacean 
Cyclops was found in water at 36° C. and turtles appeared in water 
at 44° C. (i 1 1° F.). Gudger, E. W. (Snow Worms, Nat. Hist., vol. 
23, no. 5, pp. 450-456, 1923), cites cases of Enchytraeid worms and 
other annelids besides insect larvae occurring in snow and ice. 

(5) Mountain ranges, with the factors of temperature and amount 
of oxygen available, prove most effective barriers to many forms. 
Thus, in some cases, individuals have been unable to reach new 
regions because of barriers; in other instances they reach the new 
field but are unable to survive because of lack of adaptation and 



SOCIAL LIFE OF ANIMALS 



491 



extreme competition. In the " Struggle for Existence " they perish. 
(6) Winds also prevent some dispersal of certain insects as in the 
case of the heavy trade winds. (N. A. Cobb.) 

Domestication of Animals 

Cat. — The house cats are derived from a single wild species, the 
dun wild cat, Felis ynaniculata of Northeast x^frica. There are now 
about 30 races of domesticated cats, grouped into two main classes, 
the long haired and the short haired. The Mexican hairless cat 
and the tailless Manx cat are interesting mutations. (See p. 524.) 

Horse. — The horses of today have been traced to two wild 
ancestors, Equus przewalski of Northern Asia, from which have been 
derived the Oriental, the Arabian, the Mongolian, the North African 
and the Eastern European races; the Equus caballus fossilis of 
Europe, from which have sprung the German, Norman, English 
and West European horses. In South America and in Europe, 
the bones of human beings have been found with those of horses. 
In Europe, prehistoric horses are associated with human relics of 
the Bronze Age. The New World type, Eohippus, has been found 
in the Wasatch Mts. of Western North America, in the Eocene 
period. It was about the size of a fox with four toes and a fifth 
digitary splint on each hind foot. In the middle Eocene, Orohippus 
was about 14 inches high, with four toes on its front feet and 3 toes, 
but no splints, on the hind feet. In the Oligocene period, Meso- 
hippuSy about the size of a dog or coyote, had three toes on all its 
feet. In the middle Miocene, Protohippus was the size of a Shetland 
pony, with one long toe and two short ones on each foot. In the 
Pleistocene, Equus appeared with only one developed toe and splints 
of*the second and fourth on each foot. Remains of the Old World 
type, Hyracotheriujn, have been found in the London clay and the 
Eocene formations of Europe. 

Donkeys have been derived from two wild species, the Nubian 
desert donkey, Equus taeniopus, and the onager, Equus onager, of 
Eastern Asia. The Asiatic wild ass is exceptionally fleet. There 
are today three varieties, the largest, called the kiang, found in 
Thibet and up to the snow line. The second, the ghorkkar or onager, 
found in the plains of Afghanistan, is smaller and silvery white. 
The third variety, found in Persia and Syria, is the one described in the 
Bible. The African ass is found throughout Northeastern Africa. 
It ranges westward on the deserts and is exceedingly speedy. 



492 



SOCIAL LIFE OF ANIMALS 



Dog. — The dog is supposed to be the oldest domesticated animal. 
From the savage Australian Bushman to the cultivated people of the 
world's greatest cities, we find that the dog is a companion and 
servant. He seems happiest in caring for the possessions and person 
of his master and will follow and protect the drunken sot or the filthy- 
beggar. 

There are about 200 breeds of dogs, 50 breeds being sportmg 
dogs. Theories of the origin of the dog place his ancestry as from 
the wolf or a jackal-wolf hybrid, although there are seven wild 
species which may have been contributory. The reputed ancestors 
include the jackal of Western Asia, the jackal-wolf of northeast 
Africa, the landga of India, the walgie of Thibet, and the coyote 
and gray wolf, both of America. Fossils of the American dog are 
found in the Southern Appalachian Mountains near the Cumberland 
Gap in Eastern Tennessee. 




Collie. (Photo by courtesy of James B. Vallely.) 



SOCIAL LIFE OF ANIMALS 493 

Senator Vest's Eulogy on the Dog 

" Gentlemen of the Jury: The best friend a man has in this world may- 
turn against him and become his enemy. His son and daughter that he 
has reared with loving care may become ungrateful. Those who are 
nearest and dearest to us, those whom we trust with our happiness and 
our good name, may become traitors to their faith. The money that a 
man has he may lose. It flies away from him when he may need it most. 
Man's reputation may be sacrificed in a moment of ill considered action. 
The people who are prone to fall on their knees and do us honor when 
success is with us may be the first to throw the stone of malice when 
failure settles its cloud upon our heads. The one absolutely unselfish 
friend a man may have in this selfish world, the one that never deserts 
him, the one that never proves ungrateful or treacherous, is the dog. 

" Gentlemen of the Jury: A man's dog stands by him in prosperity and 
poverty, in health and in sickness. He will sleep on the cold ground, 
when the wintry winds blow and the snow drives fiercely, if only he may 
be near his master's side. He will kiss the hand that has no food to 
offer, he will lick the wounds and sores that come in encounter with the 
roughness of the world. He guards the sleep of his pauper master as if 
he were a prince. 

"When all other friends desert, he remains. When riches take wings 
and reputation falls to pieces he is as constant in his love as the sun in 
its journey through the heavens. If fortune drives the master forth an 
outcast into the world, friendless and homeless, the faithful dog asks no 
higher privilege than that of accompanying him, to guard him against 
danger, to fight against his enemies, and when the last scene of all comes 
and death takes his master in its embrace and his body is laid away in 
the cold ground, no matter if all other friends pursue their way, there by 
his graveside will the noble dog be found, his head between his paws and 
his eyes sad, but open in alert watchfulness, faithful and true even to 
death." " 

* The dog that called forth this tribute to canine affection and fidelity was Drum, 
a foxhound, owned in Johnson County, Missouri. He was shot by a man who was 
later sued for damages by Drum's owner. Learned counsel were engaged by both 
sides and the case was finally tried before a jury in the State Circuit Court, in 1870. 
The late U. S. Senator George G. Vest made the closing plea for the plaintiff, the 
peroration of which is printed above. Court, lawyers and audience were entranced by 
it. Heavy damages were awarded the plaintiff, and Vest's Eulogy on the Dog stands 
as the most eloquent and touching tribute ever paid to man's faithful friend. Cour- 
tesy of American Humane Education Society, Boston. 



494 SOCIAL LIFE OF ANIMALS 

Pigs. — Our modern hogs are descended from two wild races, the 
European Wild Boar, Sus scro/a, and the species Sus viltatus, found 
in Eastern Asia. From the Asiatic form have descended most of 
the European races. The Chinese domesticated the hog centuries 
ago. 

Cattle. — Present races of cattle have descended from two sources, 
the wild bayiteng^ Bos sondakus, of South Asia, from which have come 
the zebus, the Egyptian longhorns and the Spanish and Alpine cattle 
of Europe; and the European wild ox. Bos primigenius, from which 
have come the English, North German and Holland cattle. The 
latter form, sometimes called the Aurochs, reached a height of 7 
feet at the withers. It had horns 6 feet in length, one of which 
held three quarts of wine. In India there now live four species of 
wild oxen closely related to the aurochs. 

Goats are descended from three wild races, Capra aegagrus, of 
Western Asia, Capra/a/coneri, and Capj-ajew/aica, of the Himalaya 
Mountains. 

Sheep originated from three wild sources, Ovis musimon of South 
Europe, Ovis tragelaphus of North Africa and Ovis ar-kal of Western 
Asia. The last named form was the ancestor of our American races. 
The species best known is the Mouflon which is still hunted in the 
mountains of Corsica and Sardinia. Early Assyrian drawings show 
fat-tailed domesticated sheep. In the Himalayas, one finds the 
great guljar or Marco Polo's sheep which ranges 18,000 feet above 
the sea in the summer. Old rams are almost white with circling 
horns, five feet on the outside curve. 

Rabbits. — There are over 70 species of rabbits, and the 15 races 
of domesticated rabbits orginated from wild species found in Spain 
and Southern France. The original European wild rabbit was 
grayish brown. 

Pigeons. — All the domestic pigeons descended from a single wild 
species, Columba livia, the common rock dove, found in Europe, Asia 
and Northern Africa. The Romans were pigeon fanciers 3,000 
years ago. Homing pigeons were used by the crusaders who sent 
messages back from the wars. 

Fowls. — Modern races of chickens are supposed by naturalists to 
be descended from the jungle fowl, Galhis bankiva, which is found 
through most of the islands adjacent to India. The heavier breeds 
are probably descended from the Malayan fowl called the Aseel. 



SOCIAL LIFE OF ANIMALS 495 

Ducks. — The wild duck, Anas boschos, the ancestor of our domes- 
tic species, is found both in China and in Europe. 

Geese are the oldest birds tamed by man. The ancestor of our 
races is Anas cinereus. The early Egyptians tamed the Nile goose, 
Chenalopex egyptiaca. 

Peacocks. — Domesticated peacocks have descended from the 
wild Indian species, Pavo cristatus. 

Turkeys have descended from two wild North American species, 
Meleagris gallopavo and a Mexican variety. We now have four wild 
sub-varieties. (Robertson.) 

Tissue Survival Outside the Body 

The pioneer in tissue culture, Dr. R. G. Harrison of Yale, showed 
many years ago that fragments of frog embryos isolated from the 
organism would develop for a number of days. His classic experi- 
ment on the development o{ neuroblasts in a hanging drop paved the 
way for much important experimentation. Montrose Burrows was 
another important figure in the development of the technique of 
tissue culture. 

Dr. Alexis Carrel, of the Rockfeller Institute, started the culti- 
vation of minute fragments from the heart of a chick embryo on 
January 17, 1912.^ Since that time he and his associates have 
carefully subdivided the culture, washed it in Ringer's solution and 
cultivated it again in a medium composed of diluted plasma. 
Carrel states that if the tissues had been able to survive for 16 years 
without trimming or hindrance, the mass would now be greater 
than that of the solar system. He emphasizes the fact, however, 
that cells massed together as a closed system must necessarily under- 
go the process of aging. 

The immortality of protozoa (see page '^i^^ is due to their ability 
to eliminate products of metabolism directly into the outside world. 

Carrel mentions the property of cell proliferation found in iris 
epithelium and thyroid epithelium, which have been cultured at the 
Rockefeller Institute for several years. 

5 Carrel, A. 1924. Tissue culture and cell physiology. Physiol. Rev., vol. 4, no. 

I, pp. 1-20. 

Fischer, A. 1925. Tissue Culture. Wm. Heinemann, London. 

Sundwall, J. 1912. Tissue Proliferation in Plasma Medium. Bull. no. 81, 
Hygienic Laboratory, U. S. P. H. S. 

Willmer, E. N. 1928. Tissue culture from the standpoint of general physiology, 
Biol. Rev., vol. 3, no. 4, pp. 271-302. 



496 SOCIAL LIFE OF ANIMALS 

E. N. Hoppe, 1928 (Tissue Culture of Guinea Pig Cardiac Mus- 
cle, Arch. Zellforsch., vol. 7, p. 352), devised a very simple 
technique for the continuous cultivation of normal tissue of mam- 
mals without the introduction of foreign plasma or other substances. 
It is uncomplicated enough to use as a routine experimental pro- 
cedure. The author has used it to study the action of toxins on 
tissues. 

Its superiority over the ordinary technique of tissue cultures lies 
in the fact that homologous plasma is used. In ordinary tissue 

Table of Longevity 
Longevity of Mammals 
Animal Reputed Age 

Elephant 30 to 80 

Horse family 15 to 40 

Rhinoceros 37 

Hippopotamus 35 

Cattle 30 

Dogs 30 

Lions, tigers 25 

Cats 23 

Giraffe 20 

Sea lions 18 

Llama 17 

Tropical fruit bat 17 

Badger I4 

Hare and rabbit 10 

Mice and rats 5 

Consult P. C. Mitchell, On longevity and relative viability in mammals and birds. 
Proc. Zool. Soc. of London, 191 1, pp. 425-548, for a more accurate report on mammals 
and birds in captivity. He records data on over 20,000 species. 

Longevity of Birds 

Animal Reputed Age 

Parrot 100 

Swan 70 

Eagle, owl 68 

Golden eagle 60 

Pelican 52 

Duck 50 

Goose 23 

Fowl 20 

Canary 20 



SOCIAL LIFE OF ANIMALS 497 

Longevity of Reptiles 

Animal Reputed A^ 

Giant tortoise loo 

Indian crocodile loo 

American alligator 40 

Boa constrictor 23 

Sphenodon, lizard 14 

Chameleon 4 

Consult S. S. Flower, Contributions to Our Knowledge of the Duration of Life 
in Vertebrate Animals. III. Reptiles. IV. Birds. Proc. Z06I. Soc. of London, 1925, 
p. 911 and p. 1365. 

Longevity of Amphibia 
Animal Reputed Age 

Frog 12 years 

Toad 2,^ years 

Longevity of Fishes 

Eel 60 years (in Roman 

ponds) 

Longevity of Arthropods 

River crayfish 20 years 

Ant 15 years 

Spider (tarantula) 15 years 

Beetle 5 years 

Queen bee 5 years 

Worker bees 6 to 8 weeks 

Longevity of Annelida 
Leech 27 years 

Longevity of Coelenterata 
Sea anemone 59 years — recorded 

The Passerine birds are extremely short lived, most of them not exceeding 5 
years in captivity. 

culture work, bird plasma is added because it lacks the blood platelets 
and therefore does not clot so quickly. (See page 457.) 

At the spring meetings of the American Association of Anato- 
mists in 1929, Dr. W. H. Lewis demonstrated moving pictures of 
rabbit ova developing in autoserum. The fertilized eggs were 
removed from the uteri at 21 to 71 hours and kept in autoserum, 
sometimes augmented by embryonic juice. 



498 SOCIAL LIFE OF ANIMALS 

Pulse Frequency 

That there is a quite definite correlation between longevity 
and rate of pulse beat was strikingly manifested to the writer on 
comparing his tables with the records furnished in Clark's studies 
on the physiology of the heart.^ The rodents with a life span of 
from 5 to lo years range in pulse frequency from 2oo to 520 pulse 
beats a minute. On the other hand the cat, known to live 23 years, 
has a pulse rate averaging about 200, while the dog, with a life span 
of 30 years, has a pulse rate of from 105 to 125 per minute. In birds 
the canary and the goldfinch, with a longevity of about 20 years, 
prove to have a pulse rate of about 1,000 per minute, but ducks and 
geese, with a longevity of 30 to 50 years, have a pulse beat of but 
150 to 300. In the cold-blooded animals, the pulse rate is much 
reduced, but a correlation exists as seen in the crocodile which is 
said to live 100 years, and which has a pulse rate of from 22 to 47 a 
minute. 

Reading this section in galley proof, O. C. Glaser stated that such 
a relationship appears to be in harmony with the results obtained 
by himself (1931) on the relation between heart beat and age in 
fishes, birds, and mammals. 

^ Clark, A. J. 1927. Comparative Physiology of the Heart. Macmillan Co., 
N. Y. 



CHAPTER XXII 

Evolution, Heredity, Eugenics 

Biologists recognize the existence of two factors responsible for 
the characteristics of living organisms. These are heredity and 
environment. 

Heredity includes what is handed on from parent to offspring. 
Sir Ray Lankester says: " Our body cells are merely a husk to pro- 
tect the germ cells until they are set free to multiply and to start 
a new individual or husk enclosing in its turn a certain number of 
cells of the initial germplasm." 

Environment, beginning before birth and continuing until 
death, includes all physical and chemical forces, acting from without 
on the germ, embryo, larva, and adult. Profound changes are 
induced before puberty, and for that matter all through life, as food- 
stuffs, temperature, oxygen and other factors stimulate or retard 
the glands of the body regulating growth and metabolism. 

The development of civilization is said to be dependent upon six 
factors: geographic or climatic conditions, race characteristics, food, 
social heredity, physical heredity and health. Studies made by the 
Army and by the United States Public Health Service indicate that 
not more than fifty per cent of our population are physically fit. 
It has been demonstrated repeatedly that with improved conditions 
of health, vice and crime diminish, civilization advances and the 
whole standard of living improves to the point where past luxuries 
become the every day equipment of a family. 

Germplasm and Somatoplasm. — For centuries observers have 
been impressed by the resemblance which children bear to their 
parents. There seems to be a transmission which is certain but 
which appears to obey no law, apparently affecting insignificant 
details and transmitting them with striking fidelity. 

Careful study of the body of an organism shows that there are 
two kinds of cells, the body cells and the germ cells. The body or 
somatic cells are those that differentiate to form the tissues of the 
body. The germ cells are those which are destined to give rise later 
to an independent organism. Both male and female germ cells 

499 



500 



EVOLUTION, HEREDITY, EUGENICS 



arise from primordial cells. Early in embryonic development it is 
difficult to tell whether these cells are to form male or female gonads. 
Cell Division. — The multiplication of cells by the process of 
cell division continues after maturity, and in most cases throughout 
life. Cell division consists of direct division or amitosis and, most 
commonly, of indirect division or mitosis. 

Direct Cell Division — Amitosis. — In this form the nucleus 
divides into two daughter nuclei without any apparent preliminary 

change in its structure. 
The division of the nucleus 
may or may not be fol- 
lowed by division of the 
cell body. 

Amitosis is found in 
the epithelium of the blad- 
der, and in the placenta. 
It is apparently normal 
in, although not exclus- 
ively characteristic of cart- 
ilage, tendon and bone- 
marrow. Some hold that 
Fig. 258. Epithelial cells from ovary of it is a sign of degeneration, 
cockroach. (From Bailey's Histology. Courtesy while Others believe it tO 
of William Wood & Co.) be a sign of rejuvenation. 

In Protozoa (page 42) it 
regularly occurs, as does mitosis also, but in the germ cells and 
in early embryonic cells division is indirect, e.g. by mitosis. 

Indirect Cell Division — Mitosis. — In this form of cell division the 
nucleus gives rise to two daughter nuclei, but only after the chro- 
matin content has undergone certain characteristic changes. 
/. Prophase: (a) As the cell prepares for division there is a 
transformation of the nuclear substance involving both physical 
and chemical changes. The chromatin loses its net-like arrange- 
ment, increases in staining power and eventually forms a definite 
number of chromosomes characteristic of the species. 

At first the chromatin is transformed into a convoluted, closely 
coiled thread, the skein or spireme. In many species a longitudinal 
split in the chromosomes becomes apparent at this time. The 
closed skein gradually opens, the nuclear membrane disappears, and 
the nucleoli are merged in the skein. In some forms the chromo- 










Fig. 259. Mitosis. A, resting cell with nucleus and true nucleolus; r, attraction 
sphere with two centrosomes. 5, early prophase. Spireme formed; nucleolus still 
present; two centrosomes connected by fibers of achromatic spindle to form amphiaster. 
C, later prophase. Spireme segmented to form chromosomes; achromatic spindle; 
polar rays; nuclear membrane fading. D, end of prophase. Monaster, with mitotic 
figure complete; chromosomes aggregated at equator of nucleus; centrosomes connected 
by fibrils of achromatic spindle. £, metaphase. Longitudinal cleavage; splitting of 
chromosomes to form daughter chromosomes, ep; n, cast-off nucleolus. F, anaphase. 
Daughter chromosomes passing along fibrils of achromatic spindle toward centrosomes; 
division of centrosomes; if, interzonal fibres or central spindle. G, late anaphase. 
Formation of diaster; beginning division of cell body. H, telophase. Reappearance 
of nuclear membrane and nucleolus; two complete daughter cells, each containing a 
resting nucleus. (From Wilson, The Cell. Courtesy of The Macmillan Co.) 



502 EVOLUTION, HEREDITY, EUGENICS 

somes develop from the nuclear reticulum without the formation of 
a spireme. 

The centrosomes move apart and about each centrosphere appears 
a group of radiating lines called the aster. Between the centro- 
spheres other lines form the spindle. The spindle and asters, stain- 
ing lightly, are called the achromatic figure, or arnphiaster. 

The chromatin thread {spireme) breaks into segments called 
chromosomes^ which group themselves in the equator of the spindle, 
forming the chromatic figure called the equatorial plate. ^ 

II. Metaphase. — The chromosomes which have split lengthwise 
now separate into two exactly similar groups. As we shall see later 
this equal distribution of chromatin has great significance. 

///. Anaphase. — As the chromosomes divide, the daughter 
chromosomes draw apart and diverge in two groups to opposite 
poles of the spindle. The two masses are connected by a bundle 
of achromatic fibers, called intej-zonal connecting fibers. In the later 
anaphase stages, the cell membrane shows signs of the constriction 
which will later produce two daughter cells. 

IV. Telophase. — The entire cell divides into two by a plane 
passing through the equator of the spindle. This is often indicated 
before division takes place by a peculiar modification of the cyto- 
plasm in the equatorial plane outside the spindle. 

Each daughter cell receives a group of chromosomes, half of the 
spindle, and one aster with its centrosome. The daughter chromo- 
somes become thickened, and form a daughter spireme, similar to 
that of the mother nucleus. 

Then the prophases are to some extent retraced, in inverse order, 
the chromosomes returning from the spireme to a chromatic net- 
work. The astral rays disappear, and the nuclear membrane 
returns.^ 

^ Heilbrunn, studying the viscosity of protoplasm in the eggs of echinoderms 
annelids and molluscs during mitosis, found two maxima of increase, one in the pro- 
phase and a second j ust prior to cleavage. Chambers, using the micro-dissection needle, 
found also that the viscosity of the aster decreases from the center towards the periph- 
ery. (Consult L. V. Heilbrunn, The Colloid Chemistry of Protoplasm. Protoplasma 
Monographieren, Geb. Borntraeger, Berlin, 1928, and The Viscosity of Protoplasm. 
Quar. Rev. of Biol., vol. 2, pp. 230-248, 1927.) 

^ In the sea urchin, 7 successive divisions, giving rise to 128 cells, may occur in 3 
hours. During the life of an individual, dividing cells are to be found at all times. 
Jolly reported that in the salamander, the prophases took 50 minutes, the metaphase 
but 4 minutes, the anaphase 48 minutes, and that reconstruction took but 39 minutes. 



EVOLUTION, HEREDITY, EUGENICS 503 

Gametogenesis {gametes, spouse; and genesis, root or origin). — 
The essential organs for reproduction are the ovaries and the testes. 
In the ovary are formed the ova, or eggs, and in the testes are formed 
microscopic elements called spermatozoa. Except in a few of the 
lower animals, the development of an ovum into a new individual 
is made possible only by its fertilization by a spermatozoon. (See 
page 506.) 

Prior to the process of fertilization there are certain preparatory 
changes which have an important bearing on the condition of the 
mature eggs and sperms. During these preliminary changes, we 
find a series of ?nitoses (see page 500) accompanied by a rather 
striking method of reduction in the number of chromosomes such 
that only one-half the original number is present in egg and sperm 
when fertilization takes place. In the body cells and the early 
germ cells, the chromosomes occur in duplicate series, one member 
of each series being derived from the male and the other from the 
female parent. The gametes (mature germ cells) each contain a 
single {hafloid) group, while the fertilized egg (zygote) contains a 
diploid group. 

Since the chromosomes are the only structures known to be 
contributed equally by the two parents and since offspring inherit 
equally from both parents, except in regard to sex and sex-linked 
characters (see page 535), the chromosomes are believed by most 
biologists to be the bearers of the hereditary determiners or genes. 
(See page 538.) Correlated with this view is the belief that each 
chromosome maintains its individuality through the various phases 
of mitosis. Evidently, then, the number of chromosomes would be 
doubled at each fertilization without some mechanism for keeping it 
constant. 

Fogg (Jour. Morphol., 1930, vol. 50) has a new and striking con- 
ception of chromatin diminution quite at variance with the texts 
and monographs now extant. He holds that the diminution of 
chromatin is not directly concerned with genetic variations, and 
plays no primary essential part in differentiating the germ line from 
the somatic. 

In Ephestia, Fogg shows that It is clearly non-genic. It is to be 
considered rather as the casting out of residual material sooner or 
later in the mitotic stages. 

Spermatogenesis (formation of spermatozoa). — The sperma- 
togonia undergo a period of multiplication by mitotic divisions (see 



504 EVOLUTION, HEREDITY, EUGENICS 

page 500) at the end of which they are transformed into Jirst spermato- 
cytes. At this time each cell increases in size and like or homologous 
chromosomes, which are already split longitudinally, become asso- 
ciated in pairs (pseudo-reduction), the usual process being a side-by- 
side synapsis, forming a quadruple chromosome known as a tetrad. 
Two of the parts are maternal and the other two, paternal in origin. 
Any two parts are known as dyads. 

Two maturation divisions follow in rapid succession without 
further splitting of the chromosomes, and separate the four parts 
of each tetrad into different cells. The two maturation divisions 
acting as a unit separate the parts of a chromosome that were 
derived from one parent from those that were derived from the 
other. This reduction (segregation) may occur at either maturation 
division. If a tetrad chromosome divides along the lengthwise 
split (equationally) at tho. first maturation division, then each dyad 
is one-half paternal and one-half maternal in origin. For such 
dyads, the second maturation division segregates the maternal part 
from the paternal. 

On the other hand, those tetrads which separated at the first 
maturation division along the line of synapsis give one dyad of 
paternal and one dyad of maternal origin. That is, segregation for 
such a pair occurs at the first maturation division, and the second 
division is consequently equational or longitudinal.^ In either case 
the four resultant cells are called spermatids, each containing one- 
half the number of chromosomes found in the original spermato- 
gonium. But while a complete haploid series is maintained, the 
spermatids differ as to the parental source of the various chromo- 
somes, now monads, the assortment being a random one. Such a 
process of segregation (reduction) is characteristic of the maturation 
divisions. 

From the spermatids develop the mature spermatozoa, each 
with a head which contains the chromosomes, a body, and a slender 
tail, used in locomotion. The question of accessory, " sex deter- 
mining " chromosomes will be discussed on page c^^Z- 

Oogenesis. — As in the development of the male germ cells, we 
find that the oogonia undergo a period of multiplication, dividing 
by ordinary mitosis (page 500). 

At the end of their preliminary mitoses, the oogonia are called 
primary oocytes. They rapidly increase in size and their longi- 

^ Both divisions are longitudinal. 



EVOLUTION, HEREDITY, EUGENICS 



505 



tudinally split chromosomes meet {synapsis) in pairs, each of which 
is composed of one maternal and one paternal chromosome. Thus 
a quadruple chromosome {tetrad) is formed as in spermatogenesis. 



SPERMATOGENESIS 



OOGENESIS 



Primordial 
Germ Cell 



Specmafo qonia 




Multiplication Period 
(Diploid Number of 
Dqad Chromosomes. 
Mantj Generations) 



Growth Period 

(Si^napsis or Union of 

Like D II ads to Form 

Ha pi old Number of 

Tetrad Chromosomes 

No DiOisions) 



First Oocijte' 



Maturation Period 
(Two DiOisions. First 
Produces Dyad Chromosome^ 
Second GiOes 
Monad Chromosomes 
Which Later 
Split 
Londltudinallu ) 

r\^ Transformation 

\yj\ Period 
C^^^j (Applies to 
■-^^ t^ale Germ 
Cells Onlij) 




Primordial 
Germ Cell 



Ooqonia 



Second Oocyte 
and First 
Polar BodlJ 



t^ature Oi/um 

and 
Polar Bodies 




Fertilization and Cleaoaae 






Fig. 260. Diagrams of spermatogenesis, oogenesis, and fertilization. Chromo- 
somes derived from female are shown in solid color, those from male in outline. Sex- 
chromosomes are shown with roughened contours. The diploid complex consists of a 
double series, both as to size and shape, with the exception that the male has only one 
sex chromosome. Note that it is always derived from his mother. (Courtesy of E. 
Carothers, 1931). 



Subsequently, in the fi7-st maturation division, the tetrads divide 
into dyads, then in the second maturation division they divide into 



5o6 EVOLUTION, HEREDITY, EUGENICS 

single components, called monads, just as in the development of the 
spermatid. 

During the first maturation division, the spindle appears near 
the periphery, and the nuclear material is divided equally, but the 
cytoplasmic material most unequally, so that the resultant budded 
''first polar body " is extremely small. It may later divide, but 
becomes degenerate and of no significance. The larger cell is called 
the secondary oocyte. 

In the second maturation division, the members of the dyads of 
the secondary oocyte are separated but the cytoplasm is again 
unequally distributed and the second polar body is given off. The 
larger cell undergoes no further changes (in contrast to the sperma- 
tid) but becomes the ^nature egg. Just as in the spermatozoa, we 
find that the eggs contain one-half the number of chromosomes 
present in the oogonia.^ 

Fertilization. — In many of the lower animals we find that fertili- 
zation takes place after the eggs are laid, but in higher forms, such 
as reptiles, birds, and mammals, it occurs in the oviduct of the fe- 
male. 

In some forms the spermatozoan enters the egg before the polar 
bodies are formed, in others it may enter after the first polar body 
is formed, but before the second has been produced, and in still 
others, maturation of the egg has been completed before a sperma- 
tozoan is admitted. Polyspermy is not unknown, but in most 
animals only a single spermatozoan penetrates the egg. 

The spermatozoan forms a jjiale pronucleus, which unites with 
the female pronucleus, and subsequent divisions are by ordinary 
mitosis. 

Two species of fishes, having different shaped chromosomes, were 
hybridized by Dr. Moenkhaus, who showed that there can be no 
question that subsequent multiplication of the cells of the fertilized 
ovum is accompanied by the equal distribution of chromatin from 
each parent. 

The chromosomes split longitudinally into two parts, separate, 
and group themselves in two clumps around the poles of a delicate 
spindle; then the cell divides. Thus by mitotic division beginning 

* Carothers, E. E. 1926. The Maturation Divisions in Relation to the Segrega- 
tion of Homologous Chromosomes. Quart. Rev. of Biol., vol. i, pp. 4I9-435. The 
sections on mitosis and gametogenesis were corrected by Dr. Carothers. 




Union of the Hdploid Groups, rertillzalm 

Zygote 






Division of the Diploid Group Mitosis 







:s^-~_'^/} 




Reduction of the Diploid Groups to Hdploid. Melosls. 

Synapsis Disjunction Haploid Groups. Qametes. 









yia.Bb.Cc.Dd. ABCd, 

Recombinations in FertlUz<ation. 



AbcD. etc 




Summary of Chromosome Behavior and Relationship 

In the germ cells, egg and sperm, the chromosomes are not paired. The four 
shown for illustration are distinguished by relative lengths. The maternal elements 
are shown In outline and identified as A, B, C, D; and the paternal in black, as a, b, 
c, d. On fertilization the zygote acquires the double or diploid number of chromo- 
somes — that is, It now has four pairs, one of each pair from the rriother (egg) 
and one from the father (sperm). The constitution of the new individual is, Aa,. 
Bb, Cc, Dd. In the course of normal cell division (Mitosis) each member of each 
pair divides into two; and each daughter cell has a full complement of chromosomes, 
continuing: the composition of the zygote. When new germ cells are being formed 
the diploid number is again reduced (Meiosis), the members of each pair going to two 
different cells — but the separation is random. Thus, the two new gametes illustrated 
show the combinations aBCd and AbcD, sixteen different combinations being possi- 
ble for four chromosomes (4-) When fertilization takes place, 
with 16 types of sperms and 16 types of eggs, mating Is random and there are 256 
possible combinations (16^), of which seven are shown. From Wilson, The Cell in 
Heredity and Development, published by The Macmillan Company." 

Fig. 261. 



5o8 



EVOLUTION, HEREDITY, EUGENICS 



I, 2, 4, 8, etc., the germinal substance is transformed by " cleavage " 
into the new organism.^ 



Cleavage and Organ Formation.- 



C^ P 





4.-'*' -;2^-N 

^-c=» §=»— / 



Gametes 




Fig. 262. Reduction Division In Relation 
to Sex Determination. (After Gruenberg, Evolu- 
tion, published by D. Van Nostrand Co., Inc.) 

The chromosomes of the male (light) parent 
(P) differ from those of the female parent (dark) 
in the form of the Y chromosome. As gametes 
are formed, one of each pair of the X chromo- 
somes (black) goes to each egg. In the forma- 
tion of sperms, however, half get the X chromo- 
some and half get the Y chromosome: there is 
only one kind of egg, but there are two kinds of 
sperms. In the following generation, Fi, the 
sperms containing the X chromosomes give rise 
to females, and those containing the Y chromo- 
somes give rise to males. Both males and 
females of this generation, however, derive half 
the chromosomes from the father and half from 
the mother. 

^ Consult the paper by H. B. Goodrich, 1929, 
Rev. of Biology, vol. 4, no. i, pp. 83-99, March. 



-Subsequent to fertilization 
certain changes take place 
converting the egg cells 
into cells that multiply and 
form the embryo. Cleav- 
age may be cotnpkfe, and 
equa/ as in Amphioxus or 
unequal as in the frog. 
On the other hand it may 
be partial, and either super- 
ficial as in the eggs of Arth- 
ropods or discoidal as in the 
chick. 

One of the most fascin- 
ating studies imaginable is 
that of organ formation 
from the primitive embry- 
onic state. It is possible 
to follow the development 
of some invertebrate types 
such as worms and molluscs 
from the one-cell stage to 
the actual development of 
complete organs. Their 
condition of semi- trans- 
parency and the distinctive 
colors of certain developing 
organs render this task 
quite easy. The nervous 
system has been traced to 
the two-cell stage in Cre- 
pidula, a mollusc, by Dr. 
E. G. Conklin. 

Germinal Layers. — 
At the end of cleavage 
(segmentation) the egg is 

Mendelian inheritance in fish. Qu. 



EVOLUTION, HEREDITY, EUGENICS 509 

divided up into cells which very early become arranged in two 
layers, the outer ectoderm (epiblast) which covers the surface of 
the embryo and the inner entoderm (hypoblast) which lines the 
interior. Between the ectoderm and the entoderm, a third layer 
of cells, the mesoderm (mesoblast), arises, usually coming directly 
or indirectly from the entoderm. 

The ectoderm gives rise to the epidermis covering the body, the 
hair and nails, and to organs derived from the epidermis-nervous 
system including the retina, epithelial lining of the mouth and anus, 
buccal glands and enamel of the teeth. 

The entoderm gives rise to the notochord and the epithelium 
lining the alimentary canal and its diverticula-including glands of 
the digestive tube, the lungs, bladder, hepatic cells of the liver and 
secretory cells of the pancreas. 

The mesoderm gives rise to structures lying between the ectoderm 
and the entoderm including all connective or supporting tissues 
except neuroglia. From it originate striated and most smooth 
muscle, blood vessels and lymphatics, peritoneum, skeleton and the 
epithelium of the genito-urinary system except the urethra and 
part of the bladder. 

Theories of Heredity and Evolution. — Hypotheses and theories 
of heredity are legion and we shall mention only a few of the older 
and less tenable ones before taking up the ones that are believed in 
at the present time. The theory of Epigenesis supposed that 
development came about through the agency of mysterious external 
forces. The theory of Preformation supposed that the germ con- 
tained all the parts that were to develop from it. We believe, how- 
ever, that the union of the germinal elements gives rise to a new 
organism that may have different qualities from the parents. We 
recognize the fact that combinations may be produced by the 
environment, and that apparently new types may be examples of 
reversion and due to the ch7~omatin that has been handed down from 
some remote ancestor. 

History of the Evolutionary Idea. — Many people have heard so 
much of the Darwinian theory of Evolution without getting any 
accurate first-hand knowledge of what Darwin said that they are 
inclined to believe that Charles Darwin gave us the first idea of 
evolution. This is far from the truth, however, since from the time 
of the earliest Greeks traditions have been handed down regarding 
the origin and development of man. 



5IO EVOLUTION, HEREDITY, EUGENICS 

The early Greeks and Romans possessed an inborn inquisitive 
spirit. They lived on the shores of the Mediterranean where many 
interesting natural phenomena were visible daily. Their speculative 
inquiry resulted in the formulation of quite definite although fre- 
quently erroneous ideas regarding the origin of life, the composition 
of matter and the reasons for extinction of some animals while 
others survived. 

Jhales (624-548 B. C.) is credited by Aristotle with the fol- 
lowing beliefs: 

I. The earth floats on the water. 1. Water is the material 
cause of all things. 3. All things are full of gods; and the magnet 
is alive, for it has the power of moving iron. 

Thales was the founder of Ionic physical philosophy and there- 
fore the founder of Greek philosophy. He discarded the mythical 
explanation of things and asserted that a physical element, water, 
was the first principle of all things. He was the first to question 
the origin of the earth, but believed that God is the mind which 
formed all things from water. 

Anaximander (611-547 B. C.) suggested the transformation of 
aquatic species into terrestrial and the especial adaptation of such 
terrestrial forms. 

Empedocles (495-345 B. C.) is called the " Father of Evolution," 
because he suggested the possibility of the oj-igtJi of t\\c fittest forms 
through chance. He thought that there were four kinds of matter, 
fire, air, earth and water, and that these were acted upon by two 
opposing forces. Love and Hate. He suggested that the independ- 
ent parts of horse and man could fuse to make a Centaur. He was 
one of the earliest students of Embryology. 

Aristotle (384-322 B. C), the most important of the Greek 
philosophers, believed in an internal perfecting tendency. He 
postulated a gradation from the mineral to the plant, the plant-like 
animal, the lower animals and finally man He said, " Nature 
makes only those fit for a purpose and makes those fit for their 
several uses." Osborn says,^ " If Aristotle had accepted Empedo- 
cles' hypothesis of the origin of the fittest through chance rather 
than through design, he would have been the literal prophet of 
Darwinism." Aristotle appealed directly to Nature for facts and 
stimulated inquiry in anatomy and physiology. As instructor of 
Alexander the Great, he secured a subsidy of 800 talents, sufficient 

6 Osborn, H. F. 1908. From the Greeks to Darwin. The Macmillan Co. 



EVOLUTION, HEREDITY, EUGENICS 511 

to support as many as 100 collectors bringing animals and plants 
from all over the known world. 

Pliny the Elder {i^-'Jf) A. D.) was a Roman who, although of 
great learning and an enthusiastic student of Nature, did more than 
any of his contemporaries to hiyider the development of the scientific 
method and spirit. He prepared 37 volumes of natural history 
and published the first cyclopedia. An honest compiler, he per- 
petuated much nonsense. Since he was considered an authority 
on natural history, his writings turned the minds of people away 
from science to books. 

From the time of Aristotle to the i6th century, the period of the 
Anatomists, Fabricius and Vesalius, anatomy and zoology were at a 
standstill. 

Galen (130-200 A. D.) was a great Anatomist whose studies on 
lower mammals were very carefully made, but who erred in con- 
cluding that the human body had the same structure. The writings 
of Galen were used as texts, and anatomy was not independently 
treated until the field was enriched by the vigorous original work of 
Vesalius. 

Vesalius (1514-1564 A. D.) published several tables of anatomy 
and in 1 543 brought out a work on the Anatomy of the Human Body, 
the earliest accurate and authoritative human anatomy. 

Studying the human subject, Vesalius raised anatomy to a 
degree of accuracy hitherto unknown. Galen, from his studies of 
the lower mammals, had taught that the lower jaw of man is divided. 
Vesalius showed on the contrary that it is a single bone in man. 
Vesalius announced, much to the discomfiture of the theologians^ 
that man had the same number of ribs as woman. When pressed 
too hard, Vesalius said that he would leave the question of an 
indestructible " resurrection bone " to be decided by the theologians^ 
as it was not an anatomical question. 

The aim in Biology in the Middle Ages was apparently devoid of 
spirit and method. Much of it was in the Medical line. Medical 
writers were concerned with healing. They had charms against 
disease. The dominant powers thought, even up to the time of 
Newton, that the devil possessed the power to give men new ideas. 

Nicholas Coperyiicus kept a fearful secret for thirty years, his 
idea that the sun and planets do not revolve around the earth, but 
that the earth revolves around the sun. 

Giordano Bruno was bolder, but after stating a similar belief 



512 EVOLUTION, HEREDITY, EUGENICS 

he was hunted from one country to another, imprisoned in the 
dungeons of the Inquisition at Rome for six years, and finally was 
burned alive because he would not recant. 

Among the first in the new liberty of the Renaissance was the 
great William Haj-vey (i 578-1657). He was graduated from Cam- 
bridge and finished his medical education at Padua under the anat- 
omist Fabricius. Vesalius, by his studies on the human body and 
his observation on the valves of the heart, and Fabricius (1537- 
1619), by his studies on the veins of the heart, had paved the way 
for Harvey's discovery of the circulation of the blood. Harvey 
lectured first on the circulation of the blood in 161 5, completed his 
work in 1616, and after years of demonstration before the Royal 
College of Physicians finally published his little book on The 
Movements of the Heart and of the Blood, in 1628. He established 
the fact that the arteries are responsible for the pulse, and that 
muscular contraction of the heart causes the circulation of the blood. 
He greatly stimulated morphological and physiological work, and 
revived the experimental method lost since the Greeks. 

John Ray (Wray) (i 628-1 705), a contemporary of Harvey, did 
excellent systematic work. He is called the " Father of Modern 
Zoology." Ray applied the term species to individuals derived from 
similar parents. He noted variations but did not conclude that 
they were of constant character. 

Just prior to Lamarck, Ray and Linnaeus defined a species^ thus 
calling attention to the characteristics of animals and plants. The 
idea of the. fixity oi species became the opinion of many biologists as 
well as theologians. A few less sheeplike clung to the idea that 
species were changeable; and were naturally ripe for the reception 
of the evolutionary hypothesis. 

Biiffon (1707-1788), while not a contributor to technical scien- 
tific literature, was of a philosophical turn and definitely popularized 
natural history. In his Histoire Naturelle he set forth the idea of 
the gradual production of different types of forms. He noted the ills 
of slavery, the presence of rudimentary organs in animals and the fact 
that in man a poor quality of food determined degenerative changes. 

Linnaeus (1707-1778), a Swede, was the founder of modern, 
systematic biologv. He established one principle that is more to his 
credit than anything else. He invented Binomial Nomenclature.^ 

' In 1623, Kaspar Bauhin published a treatise, The Pinax, in which he overthrew the 
alphabetical arrangement of plants and started the system of using two names to indi- 
cate the plant under consideration. 



EVOLUTION, HEREDITY, EUGENICS 513 

The names being in Latin, a fixed language, are understood by all 
people. Linnaeus was a systematist; Sachs calls him a " classifying, 
coordinating, sub-ordinating machine." Sachs states: "Linnaeus' 
greatest and most lasting service was in the certainty and precision 
which he introduced in the art of describing." He was behind his 
own time in Physiology, while his work in Morphology was super- 
ficial. 

Erasmus Darwin (1731-1802), the grandfather of Charles Dar- 
win, was born in England. He was a distinguished physician, 
philosopher and poet. Osborn called him the Poet of Evolution. 
He asked questions directly from Nature. " Do some of the genera 
perish by increased power of the enemies.? " " Do some animals 
change in their nature .? " " Why do plants have poisonous juices ? " 
" Many plants have arms, spines and stings for protection." 

His research and thought helped Charles Darwin. He perceived 
the significance of color for protection. "Frogs vary color accord- 
ing to environment." He noticed the adaptation o{ limbs to en- 
vironment. He saw that the strong males propagate the species and 
believed a little in the " Survival of the Fittest." With E. Darwin's 
final work in 1802 culminated the ideas of the time. He had not 
formulated any theory. He become the pioneer, setting up the 
landmarks which served as the guides for subsequent investigations. 

Jeanne Baptiste Antoine de Monet — Chevalier de Lamarck (1744- 
1829). — The name of Lamarck is intimately associated with x}lvq first 
formulated theory of Evolution. He was a contemporary of Eras- 
mus Darwin. Many of the views of Lamarck had been anticipated 
by E. Darwin. Lamarck advanced a theory in 1809 that accounted 
for variations by supposing that environment brought them about 
directly or else through the efforts made by the animal to adjust 
itself to its environment. Lamarck's theory perforce admitted 
the transmission of acquired characters. 

Haeckel says: " To Lamarck will always belong the glory of 
having worked out for the first time the theory of descent as an 
independent scientific theory of the first order and as the Philo- 
sophical foundation of the whole science of Biology." 

Lamarck's Four Laws of Evolution. — 

I. Life by its proper forces continues to increase the volume of 
every body which possesses it as well as to increase the size of 
its parts up to as great limits as it can bring itself. 



514 EVOLUTION, HEREDITY, EUGENICS 

2. The production of the new organ or part in the animal body- 

results from the supervention of a new need or want which 
continues to be felt and of a new movement which this need 
initiates and causes to continue. 

3. The development of organs and their force or power of action 

are always in direct relation to the employment of those 
organs. (Law of use.) 

4. All that has been acquired, impressed upon or altered in the 

organization of individuals during the course of their life is 
conserved by the generation and transmitted to new indi- 
viduals which have descended from those which have sur- 
vived these changes. 

Following the death of Lamarck in 1829, the theory of Evolution 
was forgotten for a time and ceased to impress the scientific world. 
Erasmus Darwin's views were not revived until the time of his 
grandson, Charles Darwin. 

Cuvier (1769-1832), the founder of Modern Paleontology, was a 
keen student of anatomy, beginning with Invertebrates. He is 
termed the founder of Comparative Anatomy, as he established a 
system of classification based on the comparative' anatomy of 
internal organization instead of the superficial external characteris- 
tics employed by his predecessors. He defended his erroneous 
" cataclysm theory," that periodically a great revolution destroyed 
all life on the earth and that a new world of unchangeable species 
arose. This theory was later, in 1832, shown to be false by Lyell, 
in his " Principles of Geology." 

Charles Darwin (1809-18 8 2). — According to Charles Dar.win, in 
1858, chance variations afford the opportunity for the factor of 
natural selection to pick out those best adapted to survive in the 
tremendous struggle for existence and the propagation of species. 

Darwin took variations for granted. His long observations, 
together with the suggestive work of Malthus on Population, con- 
vinced him of the tendency towards over-production in plants and 
animals. This, he noted, led to a struggle for existence. He pointed 
out the fact that struggle for existence might be between fellows, 
when stags fight stags in the clearing, or between foes as in the case 
of the mongoose and the snake; or finally it might be a struggle with 
fate, as in the case of " two canine animals which in time of dearth 
struggle with each other which shall get food and live." 



EVOLUTION, HEREDITY, EUGENICS 515 

The three processes, overproduction, struggle for existence and 
survival of the fittest, result in Natural Selection. Favorable adapta- 
tions enable the fit to live while the others perish. Tied up with 
these ideas was the one regarding sexual selection, in which Darwin 
attempted to show that in the birds, for example, secondary 
sexual characters such as brilliant plumage and beautiful songs 
attracted the female, who selected or chose the male. This last 
factor has been much debated, but we cannot gainsay the very 
important point that the healthy and best adapted forms, able to 
survive, will be able to reproduce. Certainly vigor exhibits itself 
in brighter color and purposeful activity. 

Darwin wrote out a sketch of his theory in 1842, and in 1844 gave 
his completed theoretical conclusions, showing the paper to his 
friends Lyell and Hooker. But the public announcement of his 
chief contribution was postponed until 1858, when he shared with 
A. R. Wallace the credit for the idea of " evolution " from the 
Natural Selection of those j'?/ to survive. 

A. R. Wallace (i 822-1913), another Englishman, was so en- 
thusiastic after reading Darwin's Journal of the Beagle Voyage in 
1845 ^hat he embarked in 1848 on an exploration of the Amazon 
and Negro Rivers lasting 4 years. Later, after he had explored in 
the Malay Archipelago, he prepared while at Sarawak (1855) a 
paper in which he concluded that every species that had come into 
existence in Nature was related to a species that preceded it. He, 
like Charles Darwin, read Malthus, On Population, and in February, 
1858, he sent Darwin a short paper entitled: "The tendency of 
varieties to depart from the original type." 

Darwin at first thought most unselfishly to present Wallace's 
paper to the Linnaean Society without comment. His friends, 
including Dr. J. D. Hooker and Sir Charles Lyell, persuaded him 
that after 20 years of careful observation had resulted in the for- 
mulation of theories backed by many facts unmarshalled by Wallace, 
the correct procedure was to present his own views in a paper to be 
read at the same symposium. 

So far as the oft-quoted idea of the survival of the fit, later para- 
phrased into Nietzsche's term the " super-man," is concerned, we 
have no finer or more noble instance of the humanity of man to man 
than that of Darwin and Wallace, the co-discoverers and crystal- 
lizers of the principle of Evolution, vying with each other over the 



5i6 EVOLUTION, HEREDITY, EUGENICS 

privilege of yielding to the other man the honor and glory of the 
public presentation of such a world-shaking hypothesis. 

Accordingly, in the spring of 1858, Sir Charles Lyell and Dr. 
J. D. Hooker communicated to the Linnaean Society Wallace's 
paper just mentioned and brief extracts from Darwin's unpublished 
works together with an abstract of a letter to Professor Asa Gray. 
The two papers, with the many striking examples supporting Dar- 
win's theory, stirred the scientific world. 

Polemics were issued by the theologians and more attention was 
thus focused than otherwise. The result was that when Darwin 
published his book in 1859, the first edition was sold out in a day. 
So bitter was the fight waged by prominent theologians that it 
took the most strenuous efforts of T. H. Huxley (i 825-1 895), the 
" bull-dog of Darwinism," and of other less militant scientists to 
turn the tide. 

When the average person thinks of " evolution " he is likely to 
confine himself to garbled statements of the Darwinian theory. 
Recently, when Bateson of England in a public address mentioned 
the fact that modern Biologists do not accept in all details Charles 
Darwin's theory, the opponents of evolution seized upon the state- 
ment and announced that the great biologist denied evolution. 
Although all biologists do not agree about the method of evolution 
they believe in it as an established law. 

A recent paper ^ by Henry Fairfield Osborn, of the American 
Museum of Natural History, points out that man has an age-old 
history. Man, we find from the discoveries of archeologists, has 
always had a religion and a soul. He has always worshipped and 
revered something, except of course during his own period of 
adolescent outbreak. 

Biologists, like other men of science, are neither atheists nor 
iconoclastic in their attitude toward religion. As the distinguished 
Sir William Bragg said (1928) in an address before the British Asso- 
ciation for the Advancement of Science, " Science is not setting forth 
to destroy the soul, but to keep body and soul together." 

Clark^s Zo'dgenesis Theory. — A. H. Clark of the Smithsonian 
Institution has formulated a most stimulating theory which he has 
been kind enough to summarize for this text. 

8 H. F. Osborn. 1928. Recent discoveries relating to the origin and antiquity of 
man. Science, vol. 65, no. 1690, pp. 481-488. 



EVOLUTION, HEREDITY, EUGENICS 517 

"While within each of the major animal groups or phyla the inter- 
relationships of the various included types as they appear in successive 
geological horizons are such that they may be represented in the form of a 
tree — the so-called phylogenetic tree — there is no real evidence, paleonto- 
logical, embryological or structural, that any of the phyla were derived 
from any of the others, although all of them must have been derived from 
a primitive single cell. Each of the phyla represents a special and definite 
structural complex basically different from the structural complex repre- 
sented by any other. 

"The protozoans differ from all other groups in the complete separa- 
tion of the cells after division. The sponges are unique in the more or 
less irregular adhesion of the cells after division in the early embryonic 
stages. All other groups pass through a gastrula or its equivalent, and 
the gastrula is the last stage common to them all. 

"It is therefore assumed that, so far as the major groups of phyla 
are concerned, evolution was a more or less simultaneous process of 
radiation from the gastrula stage, and that the phyla never were con- 
nected by intermediate types any more closely than they are at present. 

"This conclusion agrees with the determined facts of paleontology 
and embryology, and furthermore accords with our interpretation of 
conditions on the earth at and subsequent to the first appearance of life." 

Significance of the Darwinian Theory. — We owe to Darwin the 
first successful vindication of the evolution idea. It was not his 
own, nor was he its first champion, yet we think of Darwin and the 
Doctrine of Descent together. The central idea of evolution is 
that the present is the child of the past and the parent of the future. 
It is the idea of progressive change from phase to phase without 
loss of continuity. Crampton says, " The Origin of Species has 
proved a veritable Magna Charta of Intellectual liberties, for as no 
other single document before or since it has released the thoughts of 
man from the trammels of unreason, conservatism and dogma." 

Darwin's Pangenesis Theory. — Charles Darwin is responsible 
also for a theory of inheritance units. He supposed that each cell 
of the body throws off little particles which he called gemmules^ 
which are somehow gathered together in the germ cells. When these 
develop, the gemmules reproduce in the body of the new individual 
the characters of these cells of the parent from which they were 
derived. With this the transmission of acquired characters is per- 
fectly natural. The theory is called the pangenesis theory because 
it assumes that all parental somatic cells are concerned in the for- 
mation of the new individual. It is interesting to note that in spite 



51 8 EVOLUTION, HEREDITY, EUGENICS 

of the fact that Charles Darwin, like many others, ridiculed La- 
marck's laws, particularly the one that suggested the inheritance of 
acquired characters which had arisen through a new need, his pan- 
genesis theory attempts to explain the inheritance of acquired 
characters. 

As we have not yet determined the method by which somatic 
characters may be transmitted to the germ-cells, we cannot accept 
this theory. Our knowledge of the importance of biochemical 
systems such as the horrnones may increase to a point where it will 
in time be possible to accept a modified gemmule theory. 

A. Weismann (1834-19 14) in his book, The Germplasm, pub- 
lished in 1893, denied the formation of the germplasm from the body 
tissues of the individual, and maintained that its sole origin was 
from the germplasm of the parent of the individual. The germplasm, 
according to Weismann, is handed on from one individual to the 
next descendant unchanged by environment. Since the body cells 
are not inherited, there is no possibility of the inheritance of acquired 
characters. 

His theory is that sexual reproduction ^ is a mechanism for dou- 
bling the possible variations in the offspring. In such permutations 
and combinations of the qualities of the uniting germplasm, chance 
and the factor of natural selection may both become effective. 

He believed that the germplasm consists of hereditary units 
called detey-minants^ and that still smaller units called biophors are 
made up finally of molecules and atoms. As the determinants are 
grouped together to form granules of chromatin {idants) making 
up the chromosomes {ids), it is quite evident that the microscope 
cannot be used to study these units. 

Unknown Units. — Other biologists have suggested ultramicro- 
scopic units similar to the biophors and determinants of Weismann 
and the gemmules of Darwin. De Vries called them pangenes; 
Spencer named them physiological units; Galton, stirps; Hertwig, 
idioblasts; Naegeli, micellar strands; and Weisner, plasomes. We 
accept the fact that there are units which like chemical radicals are 
always found united, yet preserve their individuality in different 
combinations. How these ultramicroscopic units behave we are 
still conjecturing. 

Francis Galton (1822-1911). — A law of heredity formulated by 

' Amphimixis is biparental parentage. (See page 125.) 



EVOLUTION, HEREDITY, EUGENICS 519 

Francis Galton in 1889 seemed to some to satisfy the theoretical 
requirements. 

Gallon's Law of Ancestral Inheritance in essence was that the 
two parents between them contribute ^ of each inherited faculty, 
the grandparents together contribute ^, the great grandparents 
1/8. (The individual, i = ^ plus yi plus 1/8 plus 1/16 and so on.) 
Since this theory does not apply to individual cases and takes no 
account of prepotencies or the domination of the characters of one 
parent, it is not accepted. 

Gregor Mendel (i 822-1 884). — The Austrian monk, Gregor 
Mendel, having worked for eight years with bees and garden peas, 
in 1865 published an account of his work in the Proceedings of the 
Natural History Society of Brunn, Moravia, but this was over- 
looked until 1900 when De Vries, Correns and Tschermak, inde- 
pendently arriving at similar conclusions, brought the earlier work 
to light. In 1902, Bateson, an Englishman, pointed out its great 
importance and since then we have been much interested in experi- 
ments which seem to substantiate the early conclusions and carry 
the work on to a point where it is being applied in practical work 
with cattle, poultry and plants. 

MendeFs First Law: The Law of Dominance. — When mating 
occurs between two animals or plants unlike with reference to a 
single unit character the " hybrid-character resembles one of the 
parent forms so closely that the other either escapes observation 
completely or cannot be detected with certainty." The character 
of one parent only thus exhibited is called " dominant " while the 
other latent character is called " recessive." 

If the dominant determiner is absent, and the recessive deter- 
miner is duplicated, the recessive character is exhibited. Thus we 
may have a " dominance of recessiveness." 

When the hybrid offspring of such a cross are in turn crossed 
with each other, it is found that 25 per cent will be like the dominant 
grandparent, 25 per cent like the recessive grandparent, and 50 
per cent like the parents that resemble the dominant grandparent. 

We have therefore by crossing two DR's: yi DD plus yi DR 

plus X RR. 

When a pure dominant is crossed with a mixed dominant 
recessive, the offspring will all show the dominant character, though 
of course one-half of them are DR's. DD X DR equals 2 DD plus 
2 D (R). The DD's are pure and the D (R) is like any other hybrid 



520 



EVOLUTION, HEREDITY, EUGENICS 



and yields the i : 2 : i offspring if two are hybridized. When the 
recessive is crossed with a mixed DR we get 2 D (R) plus 2 RR. 



Mendelian Inheritance 
(Garden Peas) 



Dominant 
R. round 
Y. yellow 
T. tall 



Recessive 

W. wrinkled 
G. green 
D. dwarf 



Pure dominant crossed with pure recessive yields DR hybrids. 

Monohybrids.—R X W equals first filial generation: R (W). 

Representing the hybridization as followed by crosses of male 
and female germ cells bearing the combined R (W) we have by 
Punnett's method of squares the following Monohybrids: 



Male 




R 


W 




R 


R 


R 






R 


W 


Female 










W 


W 


W 






R 


W 



F2 generation 



This equals RR plus 2 R (W) plus WW. 
Likewise DR X DD is expressed: 

R R 

X = 2 RR plus 2 RW. 
R W 

Again, dominant-recessive DR X pure-recessive RR equals 2 DR 
plus 2 RR as: 

R W 

X =2 RW plus 2 WW. 

w w 

Complete dominance is rare, however, as Mendel discovered in the 
case of certain peculiar hybrid forms. 

{a) The law of dominance is not of universal application. 
Mendel found this true in crossing different heights of peas. 

{b) There may be an intensification of the characters of one 
parent. Brown seeded peas may be darker than the parents. 



EVOLUTION, HEREDITY, EUGENICS 521 

(c) The cross bred may have a character entirely different from 
either parent. The hybrid may possess its own character. 

In the case of the Blue Andalusian fowl we have a good example. 
The parents are: Dominant — black; recessive — white with black 
splashes. The hybrid is blue. When two hybrids are crossed the 
offspring are found to be )4 black; ^ splashed white; and }4 blue. 

MendeVs Seco7id Law: The Law of Segregation or Puj-'ity of 
Gametes^ Called the Law of the Splitting of Hybrids. — Both body 
cells and germ cells of the Fi parent, before reduction divisions, 
contain the determiners (genes) of both alternative characters and 
are hybrid in character, but during maturation the alternative 
genes (allelomorphs) are segregated, and we have the law that the 
hybrid, whatever its character, produces ripe germ cells which 
bear only the pure characters of one parent or the other. A gamete 
then is never hybrid with reference to any single character. 

Dihybrids. — The usual Mendelian proportion for crosses where 
the parents have two pairs of characteristics each is: 9 : 3 : 3 : i. 

YR crossed with GW results in offspring in the (first filial) 
generation, YR (GW). The germ cells are of four types, excluding 
the obviously impossible RW and YG,'" and may be arranged in 
squares to indicate the crossing: 

Sperm gametes YR: YW: GR: GW: 
Egg gametes YR: YW: GR: GW: 

YR YR YR YR 
YR YW GR GW 

YW YW YW YW 
YR YW GR GW 

GR GR GR GR 
YR YW GR GW 

GW GW GW GW 
YR YW GR GW 

While there are sixteen possible combinations, called genotypes, 
we must note that recessive characters are latent in the presence of 
dominant, so that we have but four types of peas so far as appearance 
goes. These are called phenotypes (see page 538). 

The possible combinations, when added together, result in 9 YR 
plus 3 YW plus 3 GR plus I GW (YWGR is really a YR, and so on). 

1" Every germ cell is pure as regards any given character. (See Second Law.) 



522 EVOLUTION, HEREDITY, EUGENICS 

There may also be a masking of characters. If gray rabbits 
are crossed with albinos, the first filial generation are all gray. The 
second filial generation become 9 gray, plus 3 black, plus 4 albinos, 
(i) Pigmentation is A and albinism is a.^^ (2) Gray is B and black is 
b. When these are crossed we get a gray hybrid. 

The gray hybrids follow the rule for dihybrids, resulting in 9 
AB (gray), plus 3 Ab (black), plus 3 aB, plus i ab (4 albinos). The 
albinos are not all the same kind, however, for we have: i aBaB, 
2 aBab and i abab. 

By crossing each type with a black we get aBaB X Ab — AB 
all gray; aBab X Ab — i AB gray plus i Ab black; abab X Ab — 
Ab all black. 

Trihybrids have three pairs of independently segregating char- 
acters. 

RYT X WGD produces the hybrid RYT (WGD). 

We must eliminate RW, YG and TD as impossible of exhibition 
(Second Law), and then we have the following combinations for 
male and female germ cells: RYT RYD RGT RGD WYT WYD 
WGT WGD. 

Placing the male germ cells in a horizontal row and the female 
germ cells in a vertical row and superimposing the squares we may 
secure 8X8 squares of possible matings or sixty-four matings. 

Results: 27 RYT plus 9 RYD plus 9 RGT plus 9 WYT plus 3 
RGD plus 3 WYD plus 3 WGT plus i WGD. 

Mender s Third Law: The Law of Independent Assortment of 
Different Allelomorphs. — " The relation of each pair of different 
characters in hybrid union is independent of the other differences 
in the two original parental stocks." 

This law becomes apparent when we try to follow the inheritance 
of more than one character at the same time. Modern investigators 
believe that the genes that show independent assortment are located 
in different chromosomes (see page 500). 

Mendel's Fourth Law: The Law of Recombination. — Mendel 
stated that " the constant characters which appear in the several 
varieties of a group of plants may be obtained in all the associations 
which are possible according to the mathematical laws of combina- 
tion." We find that the genes occur in all possible combinations 
according to the law of chance. 

1^ Where many factors are involved, it is desirable to use R for the dominant char- 
acter and r for the recessive, as is done in the case of the discussion of rabbits herewith. 



EVOLUTION, HEREDITY, EUGENICS 



5^3 



Examples of Mendelian Ikheritance in Man 



From E. G. Conklin, Heredity and Environment, 1920, pp. : 


permission of the Princeton University Press.] 


) 


Domitjant 


Recessive 


Hair 




curly 


straight 


dark 


light to red 


Eye color 




brown 


blue 


Skin color 




dark 


light 


normally pigmented 


albinism 


Countenance 




thick lower lip and prominent chin 


normal 


Temperament 




nervous 


phlegmatic 


Intellectual capacity 




average 


very great or very small 


General size 




normal size 


dwarfish 


dwarfs with short limbs but normal bodies 


normal 


and heads 




Brachydactyly: short fingers and toes 


normal 


Syndactyly: webbed fingers and toes 


normal 


Polydactyly: supernumerary fingers and toes 


normal 


Skin 




keratosis — thickening 


normal 


epidermolysis — blister form 


normal 


hypotrichosis — hairlessness and lack of 


normal 


teeth 




Nervous system 




normal condition 


epilepsy 




feeblemindedness 




insanity 




alcoholism 




criminality 




hysteria 




chorea 




St. Vitus' dance 




multiple sclerosis 


Huntington's chorea 


normal 


Eyes 




cataract 


normal 


glaucoma 


normal 



116-118. (By 



Ears 



normal 
normal 



deafmutism 

otosclerosis (rigidity of tympanum and 
hardness of hearing) 



524 EVOLUTION, HEREDITY, EUGENICS 

References 

CoNKLiN, E. G. Heredity and Environment. Princeton Univ. Press. 

Metcalf, M. M. 1911. Organic Evolution. Macmillan Co. 

Morgan, T. H. 1916. A Critique of the Theory of Evolution. Prince- 
ton Univ. Press, 

Newman, H. H. 1925. Evolution, Genetics and Eugenics. Univ. of 
Chicago Press. 

Walter, H. E. 1930. Genetics. Revised edition. Macmillan Co. 

De lories' ''Mutations-Theories— In 1901, Hugo De Vries 
(1848- ) of Holland announced that his studies of inheritance in 
the evening primrose, Oenothera Lamarckiana, had led him to con- 
clude that new species arose suddenly by what he called mutation. 
These mutants or "sports" explained the origin of a new species in 
nature. Some mutants were retrogressive and others progressive. 
Later work by R. R. Gates showed that from the cytological basis 
the new types came about through analysis of the chromatin. The 
appearance of a new type was to be explained by a change in the 
chromatin. 

Some of the workers with the fruit fly, Drosophila, once sug- 
gested that the so-called mutants of De Vries are the emergence of 
factors recessive in the ancestral stock and brought out by the 
favorable cross. The production of mutations by high temperature, 
x-rays, and other physical agents (see page 540) will give new 
impetus to cytological correlations. 

Examples of mutation include the celebrated Ancon sheep, 
which was short legged, many instances of taillessness and horn- 
lessness in cattle, and supernumerary or reduced numbers of digits 
in various animals. 

If we can eventually control the appearance or disappearance of 
factors in the germplasm, we will produce an experimental evolution. 
If not, we must confine ourselves to selection and to those influences 
of environment that tend to bring out the qualities desired. 

The Origin of New Species According to Lamarck, C. Darwin, 
A. Weismann, Mendel, and De Vries 12 

Lamarck. — New species result from variations induced by use and 
disuse. Variations are inherited directly or improved in succeeding 
generations. 

12 Modified from Locy, Biology and Its Makers. 



EVOLUTION, HEREDITY, EUGENICS 525 

C. Darwin. — Variations assumed. Variations of use are perpetuated 
by inheritance. The Jit survive and propagate. Each cell of the body 
sends off minute gemmules which enter the germ cells and transmit changes 
that have taken place in the individual. (This really admits the inher- 
itance of acquired characters.) 

Weismann. — Variations are due to permutations and combinations of 
the germplasm. Germinal selection takes place in the union of the germ 
cells. Germplasm has an unbroken continuity with an extremely complex 
organization. Body cells are not inherited. 

Mendel. — New species are due to new combinations of chromatin. 
Dominance and recessiveness are always to be considered. 

Tie Fries. — New species are due to sudden mutations or "sports." 
Mutations are sudden variations that breed true. De Vries says, a 
mutant is "a change of wide amplitude which tends to be stable because 
it involves acquisition of a new unit by the germplasm, but which is 
necessarily stable only when the individual possessing it mates with a 
similar individual." It has been suggested that mutations may occur 
through the addition or subtraction of single characters. 

Evidences for Evolution. Paleontology. — In studying the strata 
of the earth's crust we find that there is a gradual progression from 
types with primitive organization to the highly developed. Many- 
groups of animals and plants reached the climax of specialization 
at relatively early geologic periods and became extinct. 

The evolution of vertebrate classes is more satisfactorily shown 
than that of any other group, probably because they represent the 
latest phylum to evolve and most of their history coincides with the 
period within which fossils are known, while most of the inverte- 
brate phyla had already undergone more than half of their evolution 
at the time when the earliest fossil remains were deposited. 

Fossils Classified. Class i. — Actual remains of recently extinct 
animals and plants. («) In Arctic ice — the mammoth, {h) Insects 
preserved in resin-amber, (f) MolJusk shells, teeth of sharks, pieces 
of buried logs and bones of animals buried in asphalt lakes and peat 
bogs have been found in well-preserved condition. 

Class 2. Petrified fossils., seen best in plants. Class j. Casts 
and impressions. These are the impresses of soft-bodied animals 
left in mud which later solidified. The celebrated Pompeian dog 
is a striking example. The most remarkable are found in the oily 
shales of British Columbia. Even soft invertebrates are found in 
casts. 



526 



EVOLUTION, HEREDITY, EUGENICS 




EVOLUTION, HEREDITY, EUGENICS 



527 



The pedigree of the horse is the best known. Paleontological 
evidence is complete for the evolution of the horse from a five-toed 
ancestor.'^ The pedigrees of the camel and the elephant are both 
worked out quite satisfactorily also. The pedigree of man has been 
worked back successfully for many centuries with accompanying 
flint weapons and implements. 



Man 



BONES or HIND LEGS 

MonKey 




Fig. 264. Hind limb bones of man, monkey, dog, sheep and horse. (After LeConte. 

Courtesy of Amer. Mus. of Nat. Hist.) 



Evidence from Comparative Anatomy. — If we accept the Prin- 
ciple of Evolution it is easy to explain the similarity in make up of 
the wing of the bird, the foreleg of the seal and the arm of man, all 
of which are " homologous " structures. Likewise, we can explain 
the fact that man has 180 vestigial structures which now have no 
significance to him. The muscles of the human external ear and the 
subcutaneous muscles in the forehead and scalp persist, although 
useless. 

The nearest allies of man in the quadrumanous species lack a tail. 
Man has one at 6 weeks embryonic life, longer than the hinder 
limbs. Rarely, a human infant is born with a tail. The tail 
muscles persist as vestiges. The vermiform appendix of the cecum, 

13 Consult W. D. Matthew, The evolution of the horse. Quart. Rev. of Biol., vol. 
I, April, 1926. 



528 



EVOLUTION, HEREDITY, EUGENICS 



functional in the herbivores, is a menace to the health of man. A 
little blunt point projects from the inwardly folded margin or helix 
of the ear. It is the vestige of the point in lower animals. A tiny 
third eyelid is still found in man. Adult man has rudimentary hairs 
over most parts of the body. At the sixth fetal month the fetus 
has long hair over the body — " lanugo " — which in most cases is 
shed before birth. 

Evidence from Blood Tests. Precipitation Method. — Freshly 
drawn human blood is allowed to clot, then the serum drawn away. 
Small quantities of the serum are injected at intervals of one or two 

days into the veins of a rabbit and 
cause the formation in the rabbit's 
blood of an antibody, analogous to 
antitoxin obtained from a horse after 
injection of diphtheria virus. After 
the last injection, the rabbit is al- 
lowed to live several days, then is 
bled and the serum drained off and 
preserved. This is " anti-human " 
serum and is a delicate test for hu- 
man blood, not only when it is fresh, 
but even when in the form of old 
and dried blood stains. Into an 
" unknown " solution of blood, a 
few drops of the anti-human serum 
are passed, and, if the stains are hu- 
man blood, a white precipitate is 
formed and thrown down, but if 
the stains are of some domestic 
animal — pig, sheep or fowl — no such 
reaction (precipitation) occurs. This 
test is used in the detection of crime. Nuttall and others have 
shown that if sufficiently strong solutions be used and time enough 
be allowed, a relationship between the blood of all mammals is 
made evident. 

Nuttall says: " The evidence which I published upon my tests 
with precipitins shows that reactions obtained with the blood of 
Simiidae (Manlike apes) closely resemble those obtained with 
human blood, the bloods of Cercopithecidae (Old World monkeys) 
came next, followed by those of Cebidae and Hapalidae (New World 




F^MliK 



Fig. 265. Vestigial pelvic girdle 
and hind limbs of the python. 
(From Romanes, Darwin and After 
Darwin. Courtesy of Open Court 
Publishing Co.) 



EVOLUTION, HEREDITY, EUGENICS 



529 



monkeys and marmosets) which gave but slight reactions with 
antihuman serum, whilst the blood of Lemuroidea gave no indication 
of blood relationship." 

Evidence from Embryology. — All animals, even man, begin as a 
single cell, and develop in a parallel manner for a short time. We 
have considerable evidence to support the Recapitulation Theory 




Turtle N. 




C?o/eus 

F'rom inside 




Eog/e 

f^t-om ins'ide 



Young 
Duoonq ^ 




Hor^e N.j.^ 



^- Otori'a 
)■ SeQ Lion 

Ape 



P/ica, 
Semilunari-s 




Man .Man 

Fig. 266. Illustrations of the nictitating membrane in the various animals. (From 
Romanes, Darwin and After Darwin. Courtesy of Open Court Pub. Co.) 



530 



EVOLUTION, HEREDITY, EUGENICS 














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EVOLUTION, HEREDITY, EUGENICS 531 

that the history of the individual is a recapitulation of the history 
of the race, but we cannot escape the observation that there are 
notable differences, each species introducing its own specializations. 

Evidence from Classification. — The very assumption underlying 
classification is that the closest fundamental similarities between 
animals are found in those forms most closely related, and that the 
greatest differences are found in those forms that are distantly 
related. That we can place the animal kingdom in an orderly 
progressive series is an indication of such a thing as Evolution. 

Evidence from Geographic Distribution. — The evolutionary 
theory furnishes an explanation of the phenomena of distribution 
of animals and plants. A species arises at one place and spreads out 
over large areas, becoming modified as it goes, and new species are 
formed from old through modification after isolation from the parent 
stock. We find cosmopolitan groups, those with the widest dis- 
tribution being the ones to whom no barriers are sufficient to check 
migration; such as parasitic worms carried by man and other ani- 
mals; and birds able to span large bodies of water (Newman). 
Restricted groups are those to which barriers are readily set up, and 
are frequently the only remnants of a once successful fauna or flora. 
Again the faunas and floras of continental islands are what we should 
expect on the basis of former land connection with the nearest 
continent, since they are like those of the nearest mainland and 
include types most readily blown there by wind or carried on floating 
debris. 

Chief Sources of the Foregoing Summary 

Darwin, C. Origin of Species. D. Appleton and Co. 

Newman, H. H. 1925. Evolution, Genetics and Eugenics. U. of Chi. 

Press. 
NuTTALL, G. H. F. Blood Immunity and Blood Relationship. Camb. 

Univ. Press. 
Scott, W. B. 191 i. The Theory of Evolution. Macmillan Co. 
Thomson, J. A. 1909. Darwinism and Human Life. Henry Holt & 

Co. 

Sex Determination, — The theories of sex determination afford an 
opportunity to test the relative importance of the chromosomes as 
opposed to environmental influence. Since there are but two sexes, 
it must be conceded at the start that any theory of sex determination 
will appear to be right, one-half of the time. 



^2^ EVOLUTION, HEREDITY, EUGENICS 

One of the earliest known theories of sex determination, first put 
forth by Aristotle, is based on the alternate functioning of the ovaries 
and on evidence from pregnancies after one ovary has been removed. 
The right ovary is supposed to produce eggs that develop into males. 
Experiments with mammals and statistics from hospitals prove this 
theory worthless. The age and vigor of the parents have also been 
shown to be of no importance. 

In cattle, Thury, Russell and later Raymond Pearl have pro- 
duced considerable evidence to prove that matings which take place 
at the beginning of heat produce a preponderance oi females, while 
those taking place in the period of heat produce males. In pigeons 
the eggs produced in the early part of the breeding season will 
develop into males, while those from the latter part of the breeding 
season develop \x\to females. Whitman and Riddle have brought 
out this fact most clearly. 

Riddle believes that sex is a quantitative modifiable character. 
The males have a higher rate of metabolism, than the females. He 
concludes ^'^ that from the egg-stage onward through embryonic and 
adult life the oxidizing powers of the male tend to exceed those of 
the female, and that it is this tendency which ultimately decides 
whether male or female shall develop. According to Riddle the two 
diverse chromosome combinations which ordinarily determine sex 
really accomplish this by thus providing an " internal genetic pull 
toward a lower or a higher metabolic rate." This genetic tendency 
can, however, be overridden by means which specifically establish 
an opposed rate of metabolism over prolonged periods, particularly 
over early and critical periods in the differentiation of sex. 

As Riddle has pointed out (Science, 1927. vol. 65, page 139), 
Goldschmidt (Science, 1926, n. s., vol. 64, page 299) has made no 
reference to the earlier work of Riddle when (Science, 191 2, n. s., 
vol. 35, page 462) he first gave evidence for his quantitative theory 
of sex. Riddle gladly credits Goldschmidt with the discovery that 
the genes influencing sexuality in the autosomes were not of equal 
potency in certain races of moths (see Goldschmidt's Enzyme 
Theory, page 534). 

Certain Germans, including Pryll, Zolner, Ismer and Siegel, 
published papers during the Great War, indicating that earlier ova 
develop into males while the later, more mature and possibly better 

1^ Riddle, O. 1916. Sex control and known correlations in pigeons. Amer. Nat., 
vol. 50, pp. 385-410. 



EVOLUTION, HEREDITY, EUGENICS S33 

nourished ova produce females. Statistical studies negative this 
hypothesis and indicate that the sexes are. about evenly distributed 
regardless of the lunar cycle. 

Schenck suggested that the ripe eggs develop into males and the 
unripe into females. He fed women nitrogenous food, induced 
complete metabolism and males appeared, part of the time, of 
course. In wasps and other insects it is well known that an abun- 
dance of food induces greater numbers of females. In bees the 
queen is procured by special " bee bread." H. D. King has shown 
that neither food nor temperature is a factor in sex determination 
in the frog. 

In Rotifers, D. D. Whitney and others have shown that a larger 
number of male grandchildren are produced by feeding the female a 
green unicellular organism, while if she is fed a colorless organism, 
the offspring are practically all females. ShuU and Ladoff showed 
that oxygen excess produced males but Whitney contended that 
oxygen was not a factor. 

Robinson advanced the theory that the adrenals determine the 
sex of the offspring, maintaining that an excess of adrenalin pro- 
duces males, and that a smaller amount causes the development of 
females. He based his conclusions on fifty clinical cases. Experi- 
ments do not prove his theory, however. 

That there is an intimate relation between the genital glands and 
the adrenals, the pituitary and the thyroids, cannot be denied. To 
prove a specific physiological basis for the generally accepted action 
of the chromosomes is a most difficult problem. 

The Accessory or Sex Determining Chromosome. ^^ — In 1891, 
Henking found in the Hemipteran Pyrrhocoris a "peculiar chroma- 
tin-element " which passes undivided to one pole while the other 
eleven chromosomes are equally divided. He labeled it "X," and 
finally termed it a "nucleolus." 

In 1901, McClung recognized the chromatin nucleolus of Henk- 
ing as a chromosome which he traced (in the grasshopper Xiphidiu?n) 
into the first spermatocyte, where it passed undivided to one pole, 
then divided in the second spermatocyte, giving rise to two types of 
spermatozoa. McClung was the first to suggest the bearing of two 
kinds of spermatozoa on the determination of sex, and in 1902 he 
called the sex chromosome the " accessory chromosome." 

15 Consult General Cytology, Chicago Press, 1924, and Wilson, E. B., The Cell, 
1925, Macmillan and Co. 



534 EVOLUTION, HEREDITY, EUGENICS 

Miss N. M. Stevens and E. B. Wilson, working independently 
on insects, and Boveri, working on sea-urchins, found that all of the 
eggs at maturity have one extra or accessory or so-called " X- 
chromosome." The sperms are of two types, one-half containing 
the X-chromosome and the other half lacking it. Wilson clarified 
matters in 1905, showing that the female has in each of her body cells 
one more chromosome than the male, her chromosome groups con- 
taining two X-chromosomes, and those of the male containing but 
one^ while other chromosomes are distributed identically in the two 

sexes. 

Following some earlier work by others, faulty in technique. Von 
Wini water demonstrated in 191 2 that in man there are 48 chromo- 
somes in the female and 47 in the male. Oogenesis results in the 
appearance of 24 chromosomes in each matured egg (23 plus X); 
but after spermatogenesis, one-half the sperms have 23 plus X, and 
the other half have only 23. The egg fertilized by the sperm with 
the X-chromosome develops into a female, while the other type of 
sperm without an accessory chromosome produces a male at fertili- 
zation. Painter has also found the Y-chromosome, and concludes 
that the male has 46 plus X, plus Y; and the female has 46 plus 2 X. 
The Y-chromosome has apparently no significance except as the 
bearer of somatic characters. 

Goldschmidfs Enzyme Theory of Sex Determination. — Gold- 
schmidt has attempted to reconcile the fact that the gonads pro- 
duce hormones which apparently under certain circumstances are 
able to override the influence of the chromosome constitution, 
producing intersexes or even reversing the sex completely. 

Goldschmidt suggests that the X-chromosome carries the gene 
(factor) of an enzyme-producing character which determines female- 
ness, while the Y-chromosome, or possibly the cytoplasm, carries 
the gene of a male-determining enzyme. In the fertilized egg with 
two X-chromosomes, the female enzyme is present in double 
quantity and produces a female. If but one X-chromosome is 
present, the cytoplasm (or possibly the Y-chromosome) produces an 
enzyme which " overpowers " the female producer and a male 
results. Goldschmidt and others have stressed the point that the 
variability of intersexual types depends on the degree of strength 
of the two sex-producing factors or enzymes, these varying in speed 
of action. (See Goldschmidt, R., 1916, Science, n. s., vol. 43, p. 98.) 



EVOLUTION, HEREDITY, EUGENICS S3S 

Sex-Linked Characters. — Along with the accessory chromosome 
go certain " sex-linked " characters. Morgan has shown that there 
are more than loo such characters in the fruit fly. In man, we 
know of five which appear in the male when simplex and in the 
female when duplex with reference to accessory chromosomes. 
These are Gowers muscular atrophy, haemofhilia (slow clotting of 
blood), color blindness or Daltonism (red from green), nightblindness^ 
and neuritis optica (progressive atrophy of the optic nerve). These 
sex-linked characters require two determiners for t\\Q female, and but 
one for their appearance in the male. It is interesting to recall the 
fact that Charles Darwin long ago noted that male albino cats with 
blue eyes are usually deaf. 

Identical vs. Fraternal Twins. — It has long been known that 
there are two kinds of twins, one type like ordinary sisters, brothers, 
or brother and sister, coming from different eggs, and c^W^d fraternal 
twins; while the other kind, produced by the division of one egg cell, 
always appear to have the same characteristics and are always of 
the same sex. These last are called identical twins and furnish 
evidence that goes far towards substantiating the theory of sex 
determination before cell division. Likewise, studies on the arma- 
dillo, which produces from one ovum four identical offspring of the 
same sex, would seem to clinch the matter as to the time of sex 
determination. 

Earlier workers were wont to rely upon the types of fetal mem- 
branes in determining the origin of twins. The assumption that 
all monochorional twins are monozygotic and all dichorial twins are 
dizygotic has met with considerable opposition, since several remark- 
able exceptions to the rule have been reported. In a paper by 
Curtius (1930), three strikingly identical sets of dichorial twins are 
reported as monozygotic. In these cases, it is probable that the 
twinning took place during early cleavage, possibly as far back as 
the four-cell or the eight-cell stage. It could not have occurred at 
the two-cell stage, as this is not equational. Newman (1931) has 
discussed such remarkable cases, and pointed out that studying the 
finger prints of twins should be regarded only as a final check on 
diagnoses. 

References on Twins 

Curtius, Fr. 1930- Nachgeburtsgefunde bei Zwilligen und Ahnlich- 

keite-diagnosis. Arch. f. Gynakologie, Bd. 140, Heft 2 u. 3. 
Newman, H. H. 1917. The Biology of Twins. Chicago Press. 



S36 EVOLUTION, HEREDITY, EUGENICS 

Newman, H. H. 1923. The Physiology of Twinning. Chicago Press. 
Newman, H. H. 1931- The finger prints of twins. Jour, of Genetics, 

vol. 22, no. 3. 
Newman, H. H. 1931- Palm print patterns in twins. Jour, of Her., 

vol. 22, no. 2, pp. 41-48. 
Patterson, J. T. 1927. Polyembryony in animals. Qu. Rev. of Biol., 

vol. 2, no. 3, pp. 199-426. 

Hermaphroditism and the Free-Martin. — Sex intergrades or 
hermaphrodites are found in many of the Invertebrate Phyla, and in 
all classes of vertebrates. Crew has described an instance of sex 
reversal in a frog which changed from a normally functioning female 
to a male that was capable of fertilizing eggs and had 774 offspring, 
all females. Crew also described a fowl that changed from a fertile 
female to a fertile male. Riddle reported sex reversal in the pigeon. 

Intersexuality in the lower mammals is quite common. It has 
been described in cattle, sheep, pigs, goats and rabbits. Some of 
the most interesting studies have developed in connection with 
"free-martins." The "free-mariin" known for years to stock 
breeders, is an incomplete female born co-twin with a male. 

The chorionic membranes of the two embryos are fused together 
and the blood vessels anastomosed so as to produce a common 
circulation. The testis of the bull calf develops more rapidly than 
the ovary and its embryonic interstitial gland supposedly exercises a 
masculinizing influence. 

Tandler and Keller (1916) and Lillie (1916 and 1917) independ- 
ently showed that in the free-martin the twins come from two eggs. 
They concluded that the free-martin is a female whose gonads have 
been transformed into a testis-like organ by male hormones from 
her twin brother. Willier has said, " the primordium of each male 
structure developed in the free-martin gonad is present in the ovary 
at the time of sex differentiation." Bissonnette has shown that the 
free-martin began as a female and developed as such for some time, 
then became modified in the male direction internally, though almost 
never externally. 

References on Free-Martins 

Bissonnette, T. H. 1924. The development of the reproductive ducts 
and canals in the free-martin with comparison of the normal. 
Am. Jour, of Anat., vol. 22, no. 2, pp. 267-345. 



EVOLUTION, HEREDITY, EUGENICS 537 

Crew, F. A. E. 1923. Studies in intersexuality. I. A peculiar type 
of developmental intersexuality in the male of the domesticated 
mammals. Proc. Roy. Soc, B, vol. 95, pp. 90-109. II. Sex reversal 
in the fowl. Proc. Roy. Soc, B, vol. 95, pp. 256-278. 

DoMM, L. V. 1927. New experiments on ovariotomy and the problem 
of sex inversion in the fowl. Jour. Exp. Zool., vol. 48, pp. 31-174. 

Hartman, C. G. 1920. The free-martin and its reciprocal in the 
opossum, man, dog. Science, n. s., vol. 52, pp. 469-471. 

LiLLiE, F. R. 1917. The free-martin: a study of the action of sex 
hormones. Jour. Exp. Zool., vol. 23. 

LiLLiE, F. R. 1923. Supplementary notes on twins in cattle. Biol. 
Bull., vol. 44, pp. 47-78. 

WiLLiER, B. H. 1 920. Structures and homologies of free-martin gonads. 
Jour. Exp. Zool., vol. 23y PP- 63-127. 

Hen-Feathering in the Seabright Bantam. — We have elsewhere 
referred (see p. 444, Internal Secretions) to the work of Goodale and 
others in removing the ovary from the fowl, with the result that 
the bird took on the plumage and the behavior of the cockerel. 
T. H. Morgan, having observed that the cockerel of the Seabright 
bantam is normally hen-feathered, performed experiments (1915) 
which he thought furnished sufficient evidence that hen-feathering 
in the mal